
B()ok_^LL 



CopjTiglil N"- 



COl'YRlCliT DKPOSIT. 




THE ORIGINAL BABCOCK TESTER 



Modern Methods 
qf Testing Milk and 
Milk Products "^ 



A HANDBOOK PREPARED FOR THE USE OF DAIRY 
STUDENTS, BUTTER MAKERS, CHEESE MAKERS, PRO- 
DUCERS OF MILK, OPERATORS IN CONDENSERIES, 
MANAGERS OF MILK-SHIPPING STATIONS, MILK- 
INSPECTORS, PHYSICIANS, ETC. ::: ::: ::: ::: ::: 



By 
LUCIUS L. yAN SLYKE 

Chemist of the Neiv York Agricultural Experiment Station 



ILLUSTRJl'ED 



NEW YORK 

ORANGE JUDD COMPANY 

LONDON 

Kegan Paul, Trench, Trubner & Co., Limited 
1906 



LIBRARY of CONGRESS 
Two Copies Received 

JUL 6 1906 

Copyright Entry ^ 
CL^SS Ct XXc. NO. 
COPY B. 



A Copy 



SF'C53 



Copyright, 1906, bv 
ORANGE JUDD COMPANY 

All Rights Reserved 



[entered at stationers' hall, LONDON, ENGLAND] 



PREFACE 

To attain the highest degree of success in the pro- 
duction of milk and in the manufacture of its pro- 
ducts, it has become essential to acquire some knowl- 
edge of the methods of testing milk and milk products. 
The application of these methods to dairying has re- 
sulted in lifting the dairy industry to a higher plane 
of intelligence, and in effecting changes of great 
•economic importance, among which may be briefly 
mentioned: (i) Greater justice rendered milk pro- 
ducers in paying for milk according to its quality. (2) 
Prevention of large losses, once very common, in the 
manufacture of butter and cheese. (3) Improvement 
of methods of manufacture through better control of 
details. (4) Increase of yield of products made from 
a given amount of milk. (5) Improvement in the uni- 
formity and quality of manufactured dairy products. 

This little book has been prepared for the use of 
dairy students, cheese-makers, butter-makers, produc- 
ers of milk, operators in condenseries, managers of 
shipping-stations, milk-inspectors, and others inter- 
ested. Physicians who are specialists in infant- feed- 
ing will find the book useful in testing human milk as 
well as cows' milk that is modified or to be modified. 

No previous chemical training is required for oper- 
ating successfully the methods described. Any intel- 
ligent person who can labor with painstaking patience 
and appreciate the value of attention to little details 
should be able to master these methods with a rea- 



VI PREFACE 

sonable amount of work. The assistance of a trained 
teacher will, of course, make the task easier. No one, 
whatever his educational preparation, can hope to use 
these or any similar methods successfully who can 
not or will not follow instructions accurately and ex- 
ercise patience in mastering every minute detail. 

In the preparation of this work, the writer has tried 
to keep in mind the following points : ( i ) Accuracy, 
simplicity and clearness of statement. (2) Making 
prominent, as far as practicable, the reasons for each 
step in each process. (3) Emphasis of common diffi- 
culties and instructions for overcoming them. (4) Im- 
pressing students with the necessity of precision and 
care in performing ever}^ detail given. (5) Selection 
of the methods approved by experience. (6) Avoidance 
of such technical methods as require unusual skill or 
equipment. (7) Omission of unnecessary details. (8) 
Embodiment of the results of the most recent investi- 
gations. (9) The special needs of those for whose use 
the work is designed. 

The scope of this work is far from exhaustive, but 
the methods selected are given with necessary com- 
pleteness. Chemical methods, requiring elaborate 
equipment and extended special training, are purposely 
omitted. Any one desiring a full description of such 
methods can obtain it by addressing a request to the 
U. S. Department of Agriculture, Bureau of Chem- 
istry, Washington, D. C, asking for a copy of "Meth- 
ods of Analysis adopted by the Association of Official 
Agricultural Chemists." 

The methods that have been compiled here are in 
large measure the direct result of the work of our 



PREFACE Vll 

agricultural experiment stations, and afford some in- 
dication of the direction and value of the work done 
by these institutions. 

In the preparation of Chapter XIV, valuable assist- 
ance has been kindly rendered by Mr. George A. Smith, 
Dairy Expert of this station. 

L. L. Van Slyke. 
New York Agricultural 
Experiment Station, 1906. 



CONTENTS 



I 

Chemistry of Cows' Milk and Milk Products . . 1 

II 

Methods of Sampling Milk 20 

III 
The Babcock Test — Description of Apparatus and 

Materials 32 

IV 
Method of Operating the Babcock Test . . ' . . 53 

V 

Method of Testing Cream by the Babcock Test . . 69 

VI 
Methods of Testing Skim-milk, Whey, Butter, Cheese, 

etc., by the Babcock Test 78 

VII 
Methods "of Testing Acidity of Milk and Milk Prod- 
ucts 88 

VIII 
Methods of Testing the Bacterial Condition of Milk 105 

IX 
Methods of Testing Milk by Rennet-Extract and 

Pepsin 113 

X 
Methods of Testing Specific Gravity and Solids of 

Milk by the Lactometer 119 

ix 



X CONTENTS 

XI 

Methods of Testing Milk and Milk Products for Adul- 
terations 133 

XII 

The Babcock Test applied to Farm Conditions . . 143 

XIII 
Methods of Commercial Testing and Scoring of But- 
ter and Cheese 150 

XIV 
Methods of Commercial Testing and Scoring of Milk 

and Cream 174 

XV 

Arithmetic of Milk and Milk Products 185 



ILLUSTRATIONS 



PAGE 

The Original Babcock Tester ..... Frontispiece 

Composite-Sample Jars 25 

Rack for Composite Samples 26 

Sampling-Dipper 27 

Scovell Milk-Sampler 27 

Equity Milk-Sampler 27 

Milk-Testing Bottle ............ 34 

Milk-Measuring Pipette 35 

Greiner's Automatic Pipette ....... 36 

Wagner's Pipette 26 

Acid-Measure 36 

Acid-Burette and Stand 37 

Automatic Burette ^., . . . 37 

Steam-Turbine Tester . 38 

Hand-Tester 38 

Small Hand-Tester 39 

Electric Centrifuge 40 

Hydrometer for Testing Strength of Sulphuric Acid 43 

Milk-Bottle Tester 46 

Testing Accuracy of Milk-Bottle ....... 46 

Burette and Support 48 

Waste-Jar for Emptying Test-Bottles 50 

Test-Bottle Rinser 50 

Test-Bottle Draining Rack 51 

Farrington's Bottle-Cleaner — Bottle-Holder Empty . 51 

xi 



Xll ILLUSTRATIONS 

Farrington's Bottle-Cleaner — Bottle-Holder Immersed 52 

Farrington's Bottle-Cleaner — Bottle-Holder Draining 52 

Correct Way of Holding Pipette and Bottle ... 55 

Wrong Way of Holding Pipette and Bottle ... 56 

Measuring Fat-Column . 63 

Automatic Russian Pipette 67 

Russian Test-Bottle 67 

Bulb-Necked Cream-Bottle 70 

Straight-Necked Cream-Bottle 71 

Cream-Testing Scales 72 

Cream-Sampling Sieve 74 

Bottles for Testing Skim-Milk 79 

Glass Funnel for Use in Testing Butter .... 83 

Mann's Acid Test 93 

Farrington's Alkaline-Tablet Test . 96 

Spillman's Acid-Cylinder 97 

Purdue Alkali-Test 99 

Hand-Centrifuge for Sedimentation Work . . . 110 

Tube for Sedimentation Work 110 

Bausch & Lomb Electric Centrifuge 110 

International Instrument Co.'s Electric Centrifuge . Ill 

Glass for Collecting Sediment in Milk 112 

Monrad Rennet-Test 113 

Marschall Rennet-Test 115 

Quevenne Lactometer 122 

Cylinder for Lactometer 125 

Comparison of Different Specific Gravity Scales . . 126 

Richmond's Slide-Rule 130 

Butter-Trier 151 



Modern Methods of Testing Milk 
and Milk- Products 



CHAPTER I 

Chemistry of Cows' Milk and Milk Products 

The normal milk of cows contains the following 
compounds and classes of compounds : 

(i) Water. (4) Milk-sugar. 

(2) Fat. (5) Salts or ash. 

(3) Nitrogen compounds or proteids. (6) Gases. 

WATER 

The water present in milk, however much its pres- 
ence may be disguised, is the compound of hydrogen 
and oxygen with which we are everywhere familiar. 
The water in milk serves the purpose of holding in 
solution the soluble constituents of the milk, and it 
also acts as a diluent, better fitting the mixture for 
animal nutrition. 

Variation. — The amount of water normally con- 
tained in milk varies, depending upon such conditions 
as individuality, breed, stage of lactation, age, char- 
acter of food, amount of water drunk, state of health, 
etc. In the case of single milkings of individual cows, 
the water may vary from 82 to 90 per cent, or more. 
In the case of milk from herds of cows, the water 
varies less, usually ranging from 86 to 88 per cent. 



MODERN METHODS OF TESTING MILK 



The influence of breed. — The following figures, 
from the records of the N. Y. Agricultural Experi- 
ment Station at Geneva, illustrate the influence of breed 
upon the water content of milk : 



NAME OF BREED 

Holstein Friesian . 

American Holderness 

Ayrshire . . 

Short Horn 

Devon 

Guernsey 

Jersey 



Per cent, of 
■water in milk 

88.20 

87-35 

87.25 

85.70 

85-50 

85.10 - 

84.60 



The influence of lactation. — The variation of water 
in milk, as affected by advance of the lactation period, 
is illustrated by the following figures, which cover a 
period of ten months from the time of calving: 

Per cent, of 

MONTH OF LACTATION watcr in milk 

I 86.00 

2 86.50 

3 86.53 

4 86.36 

5 • . . . 86.25 

6 86.00 

7 85.82 

8 : 85.67 

9 85.54 

10 85.17 



There is noticeable a general tendency for the 
amount of water in milk to increase after the first 
three months of lactation, after which there is a con- 
tinuous decrease to the end of the lactation period. 



CHEMISTRY OF COWS MILK 3 

Total solids. — Under the general term of total solids 
or milk-solids, we indicate the constituents of the milk 
other than water (and gases). The per cent, of water 
in milk subtracted from loo gives the percentage of 
milk-solids, which include fat, proteids, milk-sugar 
and salts or ash. The amount of solids in milk varies 
with the same conditions that affect the percentage 
of water in milk, but, of course, in just the reverse 
manner. Most states orescribe a legal standard for 
milk-solids, usually 12 per cent., and milk containing 
less than the legal amount is regarded as adulterated. 

MILK-FAT 

The composition of milk-fat. — Milk-fat, also called 
butter-fat, is not a single chemical compound, but is 
a somewhat variable mixture of several different com- 
pounds called glycerides. Each glyceride is formed by 
the chemical union of glycerin as a base with some 
acid or acids of a particular kind. These glycerin-acid 
compounds, or glycerides, of milk-fat contain about 
ten different acids, some being present in small propor- 
tions. The four following acids enter most largely 
into the composition of milk-fat, in the form of their 
combinations with glycerin: Palmitic acid, oleic acid, 
myristic acid and butyric acid. The compounds, or 
glycerides, formed by the combination of glycerin and 
the acids, have special names derived from the acids; 
thus, we have palmitin (glycerin combined with palm- 
itic acid), butyrin (glycerin combined with butyric 
acid), olein, etc. Milk- fat contains, on an average, 
about 40 per cent, of palmitin, 34 per cent, of olein, 
10 per cent, of myristin, 6 per cent, of butyrin, and 



4 MODERN METHODS OF TESTING MILK 

from less than i to nearly 3 per cent, of each of the 
glycerides of other acids. Milk-fat contains about 
12.5 per cent, of glycerin in combination with the 
acids. The proportions of these constituents of milk- 
fat vary somewhat, and this variation influences the 
character of the milk-fat. Thus, palmitin and myris- 
tin tend to make milk- fat harder, while olein and buty- 
rin have the opposite tendency. 

The acids contained in milk-fat or butter-fat may 
be divided into two groups : ( i ) The acids in one 
group (palmitic, oleic, myristic, stearic, lauric) are 
insoluble in water and non- volatile, while (2) the 
other acids (butyric, caproic, etc.,) are more or less 
completely soluble in water and are volatile. These 
differences afford a practical basis for distinguishing 
pure butter from artificial butter. Of the fat-acids 
contained in butter- fat, about 87.5 per cent, consists 
of the insoluble fat-acids, while in other forms of 
animal fat (beef- fat, lard, etc.,) the amount of these 
insoluble fat-acids is considerably greater. The amount 
of volatile fat-acids in milk- fat or butter- fat is much 
greater than in other forms of animal fat. 

Fat-globules in milk. — Milk-fat is present in milk, 
not in solution, but suspended in the form of very 
small, transparent globules. Globules varying in size 
between one twenty-five hundredth and one fifteen- 
thousandth of an inch in diameter are the ones most 
commonly present. The average size of fat-globules 
in milk is somewhat more than one ten-thousandth of 
an inch in diameter. The smaller globules are more 
numerous than the larger ones. In one drop of aver- 
age milk there are more than one hundred million fat- 



CHEMISTRY OF COWS MILK 5 

globules. Skim-milk contains fewer and smaller glo- 
bules than whole ' milk, while the reverse is true of 
cream. The large globules do not differ in composi- 
tion from the small ones. -The size and number of 
fat-globules in milk are influenced by such conditions 
as advance of lactation, breed of cow, food, age, 
health, different milkings, different parts of the same 
milking, etc. 

It was formerly believed generally, and is still by 
some, that the fat-globules of milk are surrounded by 
a membranous covering, or else by a semi-liquid, al- 
buminous layer. We may, however, accept it as es- 
tablished beyond reasonable doubt that the fat-globules 
of milk have no special covering of any kind, but are 
simply minute particles of fat floating free in milk in 
the form of an emulsion. Fat-globules quite generally 
retain their individuality even in butter and cheese. 

Amount of fat in milk. — Normal milk varies greatly 
in its fat content, containing from below 2 to over 10 
per cent., if we consider single milkings of individual 
cows. The milk from herds of cows varies in fat 
more commonly between the limits of 3 and 5 per 
cent. The average amount Of milk-fat in milk pro- 
duced in this country, taking the true average for the 
entire year, lies somewhere near 4 per cent., perhaps 
a little under. Many of the conditions that affect the 
percentage of fat in milk are fairly well known, while 
others are little understood. We will briefly consider 
some of the well-recognized conditions that influence 
the fat content of milk. 

(i) Infincnce of individuality of coiv on fat con- 
tent of milk. — It is uncommon to find in a herd of 



MODERN METHODS OF TESTING MILK 



COWS t\yo individuals whose milk contains the same 
per cent, of fat, whether we consider single milkings 
or the average of many milkings. 

(2) Iniincncc of breed of cow on fat content of 
milk. — It is well know^n that the per cent, of fat in 
milk varies in a somewhat characteristic way with 
the kind of breed of covv^. While there is marked 
variation in individuals of the same breed, there is 
found to be a fairly uniform difference, more or less 
marked, if we consider the averages of several indi- 
viduals. It is largely owing to this influence that 
we find the milk of one country differing from that 
of another, or the milk of one section of a country 
differing from that of another section. For example, 
the average amount of fat in milk in Germany and 
Holland is fully one-half per cent, lower than in this 
country, because the prevailing breeds of cows there 
are those producing milk comparatively low in fat. 
The following figures, taken from the records of the 
New York (Geneva) Agricultural Experiment Station, 
represent averages of many individuals for several 
periods of lactation: Per cent, of 

fat in milk 
NAME OF BREED Average Lowest Highest 

Holstein Friesian 3.36 2.88 3.85 



Ayrshire .... 
American Holclerness 
Short Horn . 

Devon 

Guernsey .... 
Jersey 



3-6o 

444 
4.60 
5-30 
5.60 



3.20 

3-49 
4.28 
4-30 
4-51 
4.96 



4.24 
392 
456 
5-23 
6.13 
6.09 



(3) Influence of age of coiv on fat content of 
milk. — So far as published data throw light upon this 



CHEMISTRY OF COWS MILK 



point, there appears to be a tendency for milk to be- 
come less rich in fat with each succeeding period of 
lactation, especially after the second, though individ- 
ual exceptions are not infrequent. More data are 
needed to settle the question definitely. 

(4) Iniiiience of advance of lactation on the fat 
content of milk. — In general, it is found that the per 
cent, of fat in milk increases as the stage of lactation 
advances after the third month, as illustrated by the 
following data from the records of the New York 
(Geneva) Station, covering 10 months from the time 
of calving' : 



NUMBER OF 
MONTH OF LACTATION 
I 
2 

3 

4 
5 
6 

7 

8 

9 

10 



Per cent, of 
fat in milk 

4-54 

4-33 

4.28 

4-39 
4.38 
4-53 
4-56 
4.66 

4-79 
5.00 



(5) Variation of time between milkings in rela- 
tion to the fat content of millz. — As a rule, the longer 
the time between two successive milkings, the smaller 
is the per cent, of fat in the milk; and the shorter the 
time between milkings, the greater the per cent, of fat. 
When the time between milkings is uniformly equal, 
the variation of fat in milk is small, provided the gen- 
eral environment of the animal is the same. How- 
ever, as there are not commonly such entirely uniform 



8 MODERN METHODS OF TESTING MILK 

conditions of surroundings during the day and night, 
there appears to be a common tendency for the pres- 
ence of a Httle more fat in the morning's milk, even 
when milkings are apart the same length of time. 

(6) Variation of fat content in different partialis of 
milk drazvn from the udder. — The following figures, 
taken from the writer's records, illustrate the general 
rule that the first milk drawn contains least fat, the 
milk last drawn (strippings) being the richest in fat: 

Per cent, of fat in milk 
cow I cow 2 cow 3 
First portion drawn .... 0.90 1.60 1.60 
Second portion drawn . . . 2.60 3.20 3.25 
Third portion drawn .... 5.35 4.10 5.00 
Fourth portion drawn (strip'gs) 9.80 8.10 8.30 

It is also known that the per cent, of fat in milk 
varies in different quarters of the udder of a cow, and 
also varies more or less in each quarter with the order 
in which the teats are milked. 

THE NITROGEN COMPOUNDS OF MILK 

Some confusion prevails in respect to the names of 
the nitrogen compounds of milk. They have been 
spoken of as albuminoids, proteids, etc. Frequently 
the word casein is erroneously used to include all the 
nitrogen compounds of milk. 

How many nitrogen or proteid compounds are pres- 
ent in normal milk? What are they? Different work- 
ers have reported from one to seven or more. The 
chemical evidence at hand justifies us in the belief that 
fresh, normal milk contains not more than three or, 
perhaps, four nitrogen-containing or proteid bodies, 



CHEMISTRY OF COWS' MILK 9 

viz., casein, albumin, globulin and galactase. Globulin 
and g-alactase are present in so small quantities that 
we can properly regard casein and albumin, quantita- 
tively, as being essentially the nitrogen compounds of 
milk. 

Milk-Casein is the most important nitrogen com- 
pound in milk, because, (ist) it is the one present in 
largest quantity; (2d) its presence makes it possible 
to convert milk into cheese; and (3d) it has a high 
value as food. Milk-casein is most familiar to us in 
the form of the solid, white substance called curd, 
which forms in milk when it sours (though, strictly 
speaking, this well-known, white substance is not milk- 
casein, but casein lactate). 

(i) Composition of milk-casein. — Casein is a very 
complex chemical compound, containing the elements 
carbon, oxygen, hydrogen, nitrogen, sulphur, and phos- 
phorus. In milk the proteid molecule of casein is com- 
bined with calcium, or some calcium compound, and 
hence the proper chemical name of milk-casein is 
calcium casein. It exists in milk, not in solution, but 
in the form of extremely minute, solid, gelatinous par- 
ticles in suspension. The slime found in the bowl of 
centrifugal separators consists, to a considerable ex- 
tent, of milk-casein. 

(2) Action of acids npon milk-casein. — When milk 
sours in the ordinary way, the lactic acid formed acts 
upon the calcium casein, two chemical changes taking 
place. First, the lactic acid combines with the cal- 
cium of the calcium casein, forming calcium-free ca- 
sein, or simply casein set free from its combination 
with calcium. When more lactic acid forms, the sec- 



10 MODERN METHODS OF TESTING MILK 

end change takes place, the free casein combining di- 
rectly with the acid, forming casein lactate, which is 
familiar as the curd of sour milk. Similar chemical 
changes occur when milk is treated with other acids, 
such as h3^drochloric, acetic, etc. Both free casein and 
its familiar salts formed with acids are insoluble in 
water. The action of acids on calcium casein and on 
free casein is hastened by increase of temperature. 
Both casein and casein compounds with acids dissolve 
in an excess of acid, probably forming soluble casein 
salts. 

(3) Action of alkalis on milk-casein. — Dilute solu- 
tions of alkalis (caustic soda, ammonia, etc.) act upon 
casein and its salts with acids, forming compounds 
that dissolve easily in water. These alkali compounds 
of casein are not affected by rennet. Some of these 
compounds are found in commerce as food and me- 
dicinal preparations under such names as Plasmon, 
Nutrose, Santogene, Eucasein, Galactogene, etc. 

(4) Action of heat on milk-casein. — Heat alone un- 
der ordinary conditions, even at the boiling point of 
water, does not coagulate the casein in milk. Casein 
may be coagulated by heating under pressure at a tem- 
perature of about 270° F. The browning of milk 
heated under pressure is more or less due to changes 
in the casein. The formation of a peculiar skin on 
the surface of milk heated above 140° F. is largely 
due to the calcium casein of the milk and not to albu- 
min as was formerly supposed. The skin itself con- 
tains practically all of the constituents of the milk and 
may be regarded as a kind of evaporated milk. 

(5) Action of rennet on milk-casein. — One of the 
most characteristic properties of the calcium casein 



CHEMISTRY OF COWS MILK II 

of milk is its coagulation by the enzym or chemical 
ferment contained in rennet, which is an extract of the 
mucous membrane of a calf's stomach. This property 
makes possible the manufacture of cheese from milk. 
The curd formed by the action of rennet is called para- 
casein or, more properly, calcium paracasein. There 
appears to be little or no chemical difference between 
calcium casein and calcium paracasein. The coagula- 
tion of calcium casein produced by rennet is quite dif- 
ferent from that produced by acids. Calcium paraca- 
sein behaves towards acids and alkalis much like cal- 
cium casein. 

(6) Other changes caused in milk-casein. — Under 
the action of chemical reagents, of enzyms and of va- 
rious organisms, calcium casein and paracasein may be 
changed into a large number of other substances. 
Among the compounds and classes of compounds thus 
formed are paranuclein, albumoses, peptones, amides 
(crystallizable bodies) and ammonia. These products 
are never found in normal milk as it leaves the cow, 
but may be present in milk that has stood some time. 

Milk-Albumin. — Milk-albumin differs from milk- 
casein in composition and behavior. Thus, milk-albu- 
min (i) is not acted upon by rennet; (2) is not coag- 
ulated by acids at ordinary temperatures; (3) is co- 
agulated by heat alone, though not completely, above 
160° F. ; and (4) is in solution in milk. 

Milk-Globulin. — This compound is present only in 
small quantities in normal milk and is of no special 
importance, so far as known. 

Galactase. — This substance is an unorganized fer- 
ment, or a mixture of such ferments, present in normal 
milk. It somewhat resembles pepsin in its action, be- 



12 MODERN METHODS OF TESTING MILK 

ing able to coagulate milk-casein and then digest it 
or make it soluble. It is present in very small amounts 
in milk and its action is very slow. It has never been 
isolated from milk in pure form. It is probably a nitro- 
gen-containing substance. Our knowledge of galac- 
tase is very far from complete. 

Amounts of casein and albumin in milk. — In single 
milkings of individual cows, the casein and albumin, 
taken together, vary from 2.5 to 6 per cent, and 
average about 3.2 per cent. Milk-casein varies in 
amount from 2 to 4 per cent, and averages about 2.5 
per cent. Albumin varies from 0.5 to 0.9 per cent, 
and averages about 0.7 per cent. The amount of ca- 
sein in relation to albumin varies greatly. On an 
average, milk contains about 3.6 parts of casein for 
one of albumin, or, stated another way, casein consti- 
tutes about 80 per cent, of the nitrogen compounds of 
milk. 

The amount of casein and albumin in milk is influ- 
enced by many conditions, such as influence the gen- 
eral composition of the milk, among which are individ- 
uality, breed, advance of lactation, etc. As the lacta- 
tion period advances, there is a general tendency on 
the part of casein and albumin in milk to increase. 

Relation of fat and nitrogen compounds in milk. — 
In normal milk containing over 3 per cent, of fat, the 
amount of casein and albumin is rarely greater than 
the amount of fat, especially in the milk of herds of 
cows. When the per cent, of fat is less than that of 
the nitrogen compounds, the milk may generally be 
regarded as skimmed, especially in the case of milk 
from herds. 



CHEMISTRY OF COWS MILK 1 3 

MILK-SUGAR 

Milk-sugar, also called lactose, Is present in cows' 
milk in solution. In general composition, it resembles 
ordinary sugar, but it is less sweet and less soluble 
in water. The amount of sugar in milk varies from 
below 4 to over 6 per cent, and averages about 5 per 
cent. Its importance in dairy work, especially in con- 
nection with the manufacture of butter and cheese, 
comes from the ease with which it is converted into 
lactic acid by certain forms of bacteria. In the ordi- 
nary souring of milk, the amount of milk-sugar de- 
creases somewhat more than one-fourth and there is 
formed as a maximum about 0.9 per cent, of lactic 
acid. More acid may be formed after some time. 
Hence, sour milk, when two or three days old, con- 
tains only 3.5 to 4 per cent, of milk-sugar. The sugar 
of milk passes largely into the whey in cheese-making 
and forms over 70 per cent, of the solids in whey. 
The milk-sugar of commerce is usually prepared by 
evaporating whey and purifying the impure product 
first obtained. 

THE SALTS OF MILK 

The salts of milk, commonly included under the 
term "ash," are present in only small amounts, 0.7 
per cent, on the average ; but they have important 
relations to milk and its products. Our knowledge of 
these compounds is very incomplete. The salts of milk 
are commonly spoken of as the ash or mineral constitu- 
ents. This conception is somewhat misleading, be- 
cause the materials appearing in the ash of milk are, 
to some considerable extent, combined in organic com- 
pounds, instead of existing in the milk as separate 



14 MODERN METHODS OF TESTING MILK 

inorganic bodies. The ash represents in amount, 
therefore, more than the so-called mineral constitu- 
ents of milk and less than the salts of milk. While 
the ash in milk amounts to about 0.7 per cent., the 
amount of salts probably approximates 0.9 per cent. 
A portion of the salts of milk is in solution, including 
such compounds as calcium citrate, sodium chloride, 
potassium acid phosphate, etc., while a portion (tri- 
calcium phosphate) appears to be in suspension in 
the form of very finely divided particles. 

THE GASES OF MILK 

Milk contains more or less oxygen and nitrogen, 
these gases being carried into it mechanically from 
the air in the process of milking. It contains also, 
when freshly drawn, carbon dioxide, already present 
in the udder milk, there being probably between 3 and 
4 per cent, by volume, a portion of which escapes at 
once while being drawn from the udder under usual 
conditions. 

GENERAL SUMMARY 

Milk contains water, fat, casein, albumin, sugar, 
salts, carbon dioxide and some other constituents in 
small quantities. The fat and casein and some of the 
salts are in suspension and not in solution, while al- 
bumin, sugar and the larger portion of the salts are 
held in solution by the water. 

As a matter of convenience, the compounds of milk 
are divided into certain arbitrary groups. By one 
system of division, the compounds of milk are ar- 
ranged in two classes: — (i) Water, and (2) inilk- 
solids (or total solids), this second class including 



CHEMISTRY OF COWS MILK 



15 



fat, casein, albumin, sugar, salts (ash), etc. Another 
division is made on the basis of the milk-fat into (i) 
fat and (2) milk-seriun, which includes all the milk 
constituents except the fat. Separator skim-milk is 
nearly pure milk-serum. Then we have the milk- 
solids subdivided into (i) fat and (2) solids-not-fat 
(casein, albumin, sugar, salts (ash), etc.) 

The following arrangement shows the general rela- 
tion of the compounds contained in milk, the figures 
indicating the percentages present in average milk: 



Water 

87.1 



Fat 
3.9 



MILK. ^ 12.1 



Solids^ Solids-not-fat 



9.0 



r Nitrogen 
compounds 
3.2 

j Milk-sugar 
5.1 
Ash (salts) 
0,7 



f Casein, 
I 2.5 

I Albumin, etc. 
t 0.7 



Carbon dioxide 
Gases -^ Nitrogen 
Oxygen 



A^^RAGE ANALYSIS OF COWS MILK 





WATER 


TOTAL 
SOLIDS 


FAT 


CASEIN 


ALBU- 
MIN 


SUGAR 


ASH 


Average of 5,552 
American an- 
alyses c o m- 
piled by the 


Per cl. 
87.1 

87.4 


Per ct. 
12.9 

12.6 


Per ct. 
3.9 

3.75 


Per ct. 

2.5 

2.45 


Per ct. 

0.7 

0.7 


Per ct. 
51 

5.0 


Per ct. 
0.7 

0.7 


Average cheese- 
factory milk 
for the season 
(May to Nov.) 
in N.Y. State... 



i6 



MODERN METHODS OF TESTING MILK 



REPRESENTATIVE ANALYSES OF PRODUCTS AND BY-PRODUCTS OF MILK 





TOTAL 






ALBU- 




WATER 


SOLIDS 


FAT 


CASKIN 


MIN 


SUGAR 


Per ct. 


Per ct. 


Per ct. 


Per ct. 


Per ct. 


Per ct. 


13.0 


87.0 


83.5 


1.0 




.... 


36.8 


63.2 


33.75 


23.75 2 








90.3 


9.7 


0.10 


2.75 


o.eo 


5.25 


93.4 


6.6 


0.35 


0.10 


0.75 


4.80 


90.6 


9.4 


0.13 


2.80 


0.80 


4.40* 



Butter. 



Cheddar Cheese 

(green) 
Skim-milk 

(separator) 



Whey 

Buttermilk 



Per ct. 
2.5 1 

5.73 
0.80 
0.60 
0.70 



1 Salt. 2 Paracasein. ^ Salt and Ash. * .60 per cent, lactic acid in addition. 



DEFINITIONS AND STANDARDS OF MILK AND 
MILK PRODUCTS 

The United States Department of Agriculture has 
estabHshed official standards for purity of dairy and 
Other food products, defining also what is meant by the 
terms used in designating different materials. These 
definitions and standards have been most carefully 
worked out by members of the Association of Official 
Agricultural Chemists, several years having been de- 
voted to the collection of data. The official definitions 
and standards relating to milk and milk products are 
as follows : 

MILK 

Definitions. — i. Milk (ivholc milk) is the lacteal 
secretion obtained by the complete milking of one 
or more healthy cows, properly fed and kept, exclud- 
ing that obtained within fifteen days before and five 
days after calving. 

2. Blended milk is milk modified in its composition 



CHEMISTRY OF COWS MILK 1/ 

SO as to have a definite and stated percentage of one 
or more of its constituents. 

3. Skim-milk is milk from which a part or all of 
the cream has been removed. 

4. Buttermilk is the product that remains when but- 
ter is removed from milk or cream in the process of 
churning. 

5. Pasteurised milk is milk that has been heated 
below boiling but sufficiently to kill most of the act- 
ive organisms present and immediately cooled to fifty 
degrees (50°) Fahr. or lower to retard the develop- 
ment of their spores. 

6. Sterilised milk is milk that has been heated at 
the temperature of boiling water or higher for a length 
of time sufficient to kill all organisms present. 

7. Condensed milk is milk from which a considera- 
ble portion of water has been evaporated. 

8. Szveetened condensed milk is milk from which 
a considerable portion of water has been evaporated 
and to which sugar (sucrose) has been added. 

9. Condensed skim-milk is skim-milk from which 
a considerable portion of water has been evaporated. 

Standards. — i. Standard milk contains not less than 
twelve (12) per cent, of total solids, not less than eight 
and one-half (8.5) per cent, of solids-not-fat, and not 
less than three and one-quarter (3.25) per cent, of 
milk- fat. 

2. Standard skim-milk contains not less than nine 
and one-quarter (9.25) per cent, of milk-solids. 

3. Standard condensed milk contains not less than 
twenty-eight (28) per cent, of milk-solids, of which 
not less than one-fourth is milk-fat. 



l8 MODERN METHODS OF TESTING MILK 

4. Standard sivectcncd condensed milk contains not 
less than twenty-eight (28) per cent, of milk-soUds of 
which not less than one-fourth is milk-fat. 

MILK-FAT OR BUTTER-FAT 

Definition. — Milk-fat or butter- fat is the fat of 
milk. 

Standard. — -Standard milk-fat or butter-fat has a 
Reichert-AIeissl number not less than twenty- four (24) 
and a specific gravity not less than 0.905 (-^^) 

CREAM 

Definitions. — i. Cream is that portion of milk, rich 
in butter-fat which rises to the surface of milk on 
standing, or is separated from it by centrifugal force. 

2. Evaporated cream is cream from which a consid- 
erable portion of water has been evaporated. 

Standard. — Standard cream contains not less than 
eighteen (18) per cent, of milk- fat. 

BUTTER 

Definitions. — i. Butter is the product made by 
gathering in any manner the fat of fresh or ripened 
milk or cream into a mass, which also contains a small 
portion of the other milk constituents, with or with- 
out salt. 

2. Renovated or process butter is the product made 
by melting butter and reworking, without the addition 
or use of chemicals or any substances except milk, 
cream or salt. 

Standards. — i. Standard butter contains not less 
than eighty-two and five-tenths (82.5) per cent, of 



CHEMISTRY OF COWS MILK I9 

butter-fat. By acts of Congress approved August 
2, 1886, and May 9, 1902, butter may also contain 
additional coloring matter. 

2. Standard renovated or process butter contains not 
more than sixteen (16) per cent, of water and at least 
eighty-two and five-tent4is (82.5) per cent, of but- 
ter-fat. 

CHEESE 

Definitions. — i. Cheese is the solid and ripened pro- 
duct made by coagulating the casein of milk by means 
of rennet or acids, with or without the addition of 
ripening ferments and seasoning. By act of Congress, 
approved June 6, 1896, cheese may also contain addi- 
tional coloring matter. 

2. Whole-milk or full-creani cheese is cheese made 
from milk from which no portion of the fat has been 
removed. 

3. Skim-milk cheese is cheese made from milk from 
which any portion of the fat has been removed. 

4. Cream-cheese is cheese made from milk and 
cream, or milk containing not less than six (6) per 
cent, of fat. 

Standard. — Standard zvhole-milk or full-cream 
cheese contains, in the water-free substance, not less 
than fifty (50) per cent, butter-fat. 

MISCELLANEOUS MILK PRODUCTS 
Definitions. — L Whey is the product remaining af- 
ter the removal of fat and casein from milk in the pro- 
cess of cheese-making. 

2. Kumiss is the product made by the alcoholic fer- 
mentation of mares' or cows' milk, with or without the 
addition of sugar (sucrose). 



CHAPTER II 



Methods of Sampling Milk 

Too much emphasis can not be placed upon the im- 
portance of taking for analysis a sample of milk that 
truly represents the whole body of milk from which 
the sample is taken. This statement applies equally 
to any product or by-product of milk that is to be 
tested. Before a sample for testing is taken, the body 
of milk from which the sample is to be drawn should 
be uniform throughout in composition. Several con- 
ditions may disturb the desired uniformity of compo- 
sition of a mass of milk, among which are the fol- 
lowing : 

(i) Separation of fat. 

(2) Partial churning of fat. 

(3) Freezing of milk. 

(4) Souring of milk. 

SAMPLING MILK WHEN FAT HAS SEPARATED 

The rapidity with which fat-globules rise to the 
surface of milk in the form of cream is well known. 
Therefore, milk standing at rest soon loses its uni- 
formity of composition, the upper layers containing 
more fat than the lower ones. On this account it is 
always necessary, just before taking a sample of 
milk for testing, to make sure that the body of milk 
to be tested has an even composition throughout. 

Milk in which fat separation is slight. — In milk 



METHODS OF SAMPLING MILK 



21 



in which there is no visible separation of cream, even- 
ness of mixing may be best effected by pouring the 
milk from one vessel to another several times immedi- 
ately before each sample is drawn for testing. Stir- 
ring milk, as with a dipper, is less effective than 
pouring. 

Milk in which fat separation is marked. — In milk 
in which the cream has separated in a visible layer, 
the pouring needs to be done a greater number of 
times than in cases where the separation of cream is 
not noticeable ; and, in order to prevent possible churn- 
ing of particles of cream, the agitation should be as 
gentle as may be consistent with thorough mixing. 

Milk containing dried cream. — In cases where the 
cream is somewhat dried or hardened, the milk should 
be warmed to 105° or 110° F. for 5 or 10 minutes 
to allow the cream to melt. The milk is then vigor- 
ously agitated and immediately sampled. 

SAMPLING MILK WHEN FAT IS PARTIALLY 
CHURNED 

Milk-fat may separate from milk in the form of 
small butter-granules, as (i) when the mixing or 
shaking of the sample to be tested is done too vio- 
lently; (2) when milk in cans is excessively agitated 
in transportation; and (3) when bottles, partly full 
of milk, are sent by mail or express. In such partially 
churned milk it is difficult to get a representative 
sample, and the results of testing are, at best, only 
approximate, unless special measures are resorted to 
in sampling. 

Distributing fat by warming. — In the case of par- 



22 MODERN METHODS OF TESTING MILK 

tially churned milk, the fat may be redistributed in 
the milk by warming it to 105° or 110° F. long enough 
to melt the butter-granules, after which the sample 
is vigorously shaken, until the fat is evenly distributed 
through the milk, and then the sample is drawn at 
once for analysis. 

Dissolving fat in ether. — Another method of treat- 
ing partially churned milk, previous to sampling, is 
to shake the milk with 5 per cent, of its volume of 
ether until the fat-granules are redissolved and then, 
after further vigorous shaking, to take the sample at 
once. In this case it is necessary to make a correc- 
tion by adding to the results 5 per cent, or one-twenti- 
eth of the result obtained. For example, a milk, 
treated with 5 per cent, of ether, and giving, on test- 
ing, 3 per cent, of fat, should have added .15 (5 per 
cent, of 3), making the corrected result 3.15 per cent. 
When ether is used, extra care must be observed in 
mixing the acid and milk, (see p. 58) as the heat de- 
veloped may cause the ether to boil up out of the 
neck of the test-bottle. 

Measures for preventing the churning of fat in 
milk. — It is better to prevent the churning of fat in 
milk than to be put to the extra trouble required to 
get a good sample from milk that has in it fat-granules. 
Cans of milk, when necessarily exposed to much mo- 
tion in transportation, should be made as nearly full 
as possible. In the case of bottles of milk sent by 
mail or express for analysis, the churning of fat may 
be prevented in the following manner: Fill the bot- 
tle full of milk to overflowing. Then push in tightly 
a stopper of cork or rubber in which has been made 



METHODS OF SAMPLING MILK 23 

from top to bottom a hole one-eighth inch in diameter 
or less. Finally, push a close-fitting plug of wood or 
a glass rod into the hole in the stopper. 

SAMPLING FROZEN MILK 

Frozen milk is of very uneven composition in dif- 
ferent portions of its mass. The crystals of ice con- 
tained in it consist largely of water, while the liquid 
portion contains most of the milk-solids. In such 
cases it is necessary to melt the frozen portion by 
warming, and then to mix well by gentle pouring 
from one vessel to another, after which the sample is 
at once taken for testing. 

SAMPLING MILK COAGULATED BY SOURING 

A sample of thickened, sour milk can not, without 
special treatment, be taken so as to give reliable results 
in fat determination. In ordinary curdled milk the 
percentage of fat remains unchanged in amount, but 
it is not evenl}^ distributed through the milk. In pr- 
der to overcome this difficulty, the curdled casein 
lactate must be dissolved before sampling. This is 
done by adding to the milk a strong solution of caus- 
tic soda or potash (lye), or strong ammonia water, 
to the extent of 5 or lo per cent, of the volume of the 
milk used for sampling. The alkali is shaken with 
the milk until the mixture becomes completely liquid, 
after which the sample is at once drawn for testing. 
It is necessary to make a correction by adding to the 
results 5 or 10 per cent, of the amount of fat found, 
according to the amount of alkali solution used. In 
place of using a solution of alkali, one can add, in 



24 MODERN METHODS OF TESTING MILK 

small portions at a time, finely powdered caustic soda 
or potash, allowing the milk to stand some time after 
each addition of powdered alkali and shaking vigor- 
ously, the additions of alkali and the agitation being 
continued only until the milk becomes completely liquid. 
In using the alkali in solid form, no correction of re- 
sults needs to be made. The alkali solution or tab- 
lets described on page 96 may be used. A darkening 
of the milk by alkali may occur without affecting the 
results of the test. In testing, caution must be ob- 
served when adding sulphuric acid (see p. 56) to milk 
in which an alkali has been used, since an unusual de- 
gree of heat is produced and the contents of the test- 
bottle may spurt out. The acid must be added slowly 
and mixed with the milk much more deliberately than 
usual. 

COMPOSITE SAMPLING OF MILK 

Composite samples of milk. — A mixture of daily 
samples of milk, taken from day to day for several 
days in succession, is known as a composite sample. 
In commercial work at creameries, cheese-factories, 
milk-shipping stations, etc., where the number of pa- 
trons is large, a daily test of the milk for its fat con- 
tent is impracticable: To obviate the great amount of 
work involved in making daily tests, a jar is provided 
for the milk of each patron and in this jar is placed 
a sample of each day's milk, when it is delivered, these 
daily samples being mixed and allowed to accumulate 
for a period of one or two weeks. A determination 
of fat in such a composite sample gives the average 
percentage of fat in the milk for the period covered 



METHODS OF SAMPLING MILK 



25 



by the mixture of daily samples. This method has 
been proved to be as accurate as that of testing each 
sample daily by itself, but there are several precau- 
tions to be observed carefully in applying this method 
in commercial practice. 

The conditions that are necessary for success in 
using the method of composite sampling may be con- 
sidered under the following heads : ( i ) Systematic 





FIG. I 
COMPOSITE-SAMPLE JAR 



FIG. 2 
COMPOSITE-SAMPLE JAR 



preparation, (2) methods of taking daily samples, (3) 
use of preservatives, (4) care of composite samples, 
(5) ^S^ of composite samples, and (6) preparation of 
composite samples for sampling and testing. 

Systematic preparation for taking composite sam- 
ples. — A round glass jar or bottle, holding a pint or 
quart, should be provided for each patron. The forms 
given in Figs, i and 2 are suitable, or ordinary Mason 



26 



MODERN METHODS OF TESTING MILK 



fruit- jars may be used. Whatever form of composite- 
sample jar or bottle be used, the stopper or cover 
should fit perfectly tight, so as to prevent any possi- 
ble evaporation of water from the sample of milk, 

and care should be 
taken to keep the 
covers or stoppers 
tight. Each sam- 
ple-bottle or jar 
should be labeled 
with a name or 
number easily iden- 
tifying the patron 
furnishing the milk. 
The jars should be 
arranged in definite 
order on a rack 
(Fig. 3), placed 
conveniently near the point where the milk is deliv- 
ered. As explained later, some preservative is used 
in each jar. 

Taking daily samples for composite samples. — 
Each day when milk is delivered, the sample should 
be taken immediately after the milk has been poured 
into the weighing can before weighing, and should 
then be placed at once in the composite jar or bottle 
prepared for it. Two methods of sampling are in 
common use, (i) by means of a small dipper, and (2) 
by means of a sampling-tube. 

(i) TaJ?{jig sample zvith dipper. — A half-ounce dip- 
per (Fig. 4) is used for taking the sample from the 
weigh-can, as soon as the milk is poured in. The 




FIG. 3- 



-RACK FOR COMPOSITE SAMPLES 



METHODS OF SAMPLING MILK 



27 



sample is at once placed in its proper jar or bottle. 
Providing the milk is thoroughly mixed in the weigh- 
can and the quantity of milk delivered by a patron 




FIG. 4- 
SAMPLING-DIPPER 



FIG. 5 
SCOVICLL SAMPLER 



FIG. 6 
EQUITY SAMPLER 



from day to day does not vary much, this method of 
sampling gives correct results. 

(2) Taking sample zuith sampling-tube. — There are 
different types of sampling-tubes (Figs. 5 and 6), of 
which the Scovell sampler is one of the best. In this 



28 MODERN METHODS OF TESTING MILK 

instrument the main tube is open at both ends, the 
lower end closely fitting into a cap furnished with 
three elliptical openings. When the sampler, open at 
the bottom, is let down into a can of milk, the liquid 
pours into the openings and fills the tube to the height 
of the milk in the can. When the cap comes in con- 
tact with the bottom of the can, the tube slides down 
and closes the openings, after which the tube can be 
withdrawn and its contents emptied into the com- 
posite jar. 

The tube method of sampling possesses two marked 
advantages over the dipper method : ( i ) It always 
takes an aliquot portion, or uniform proportion, of 
the milk, representing a small column of the milk 
from top to bottom; and (2) it provides a strictly rep- 
resentative sample of the milk, even when sampling 
is delayed, because it takes a uniform amount from 
each layer of milk, going from too to bottom. 

THE USE OF PRESERVATIVES IN COMPOSITE 
SAMPLES 

The successful use of composite samples is made 
possible only by the presence of some substance which 
will keep the milk from curdling. Three preserva- 
tives have been found especiall}- useful for this pur- 
pose : (i) Corrosive sublimate, (2) formalin, and 
(3) bichromate of potash. 

Corrosive sublimate, known chemically as mercuric 
chloride, has the advantage of being a more powerful 
antiseptic than the other substances, much smaller 
quantities being effective in keeping milk longer, but 
it has the disadvantage of being a violent poison. 



METHODS OF SAMPLING MILK 29 

When this is used as a milk preservative, it is a wise 
precaution to add a Httle coloring matter to the milk 
in order to warn every one of its abnormal character. 
Corrosive sublimate,- mixed with coloring matter, is 
put up in convenient tablet form and has found exten- 
sive use in preserving composite samples. All things 
considered, it is probably the most satisfactory of the 
preservatives commonly employed. 

Formalin is a liquid containing about 40 per cent, 
of the chemical compound known as formaldehyde. It 
is an efifective antiseptic and has the advantage of 
being in liquid form. One cubic centimeter of forma- 
lin should keep a pint or quart sample of milk two 
weeks or more. Formalin possesses the disadvantage 
of so hardening the milk-casein that it is not as readily 
dissolved by sulphuric acid (see p. 58) as is the casein 
of untreated milk. An excessive use of corrosive sub- 
limate may produce a similar hardening of casein. 

Bichromate of potash, also called potassium bichro- 
mate, is extensively used in preserving samples of 
milk for testing. It is best to use it in powdered form. 
It has the following advantages : ( i ) It is compara- 
tively inexpensive. (2) It colors milk yellow and thus 
shows its presence. (3) It is not a very violent poison, 
though not entirely harmless. (4) It is efficient in 
keeping milk for one or two weeks. However, it has 
some disadvantages as a preservative of composite 
samples of milk: (i) If too much bichromate is used, 
the solution of the casein in sulphuric acid is some- 
what difficult and the final results of testing may not 
be clear. (2) In hot weather, it is often difficult to 
keep samples without using an excessive amount of 



30 MODERN METHODS OF TESTING MILK 

bichromate. (3) Lactic acid in milk considerably re- 
duces the efficiency of bichromate in preserving milk. 
(4) Samples of milk preserved with bichromate are 
apt, when exposed to light, to form a tough skin on 
the surface, which interferes with proper sampling. 

The amount of potassium bichromate to be used in 
composite samples is about 8 or 10 grains for half a 
pint to a pint of milk. The bichromate is put up for 
sale in tablets of convenient size, ready for use in pre- 
serving milk samples. Bichromate can be satisfactor- 
ily used even in hot weather, if the samples are kept 
in a dark, cool place most of the time. 

CARE OF COMPOSITE SAMPLES 

Li caring for composite samples "of milk or cream, 
some special precautions must be observed, (i) Com- 
posite sample jars must be kept covered tight to pre- 
vent evaporation of water, which would result in giv- 
ing a test for fat higher than the correct amount. (2) 
They should be kept in a cool place, so that the small- 
est possible amount of preservative will need to 
be used. (3) They should be kept in the dark 
most of the time, since direct sunlight may cause 
the formation of a tough cream, rendering difficult 
the taking of a good sample for testing. (4) When 
the daily sample of milk is added to the composite 
sample, the contents of the jar should be mixed by 
giving the jar a gentle, rotary motion. Unless this 
is done regularly each day, the cream that rises be- 
comes tough, especially where it is in contact with the 
sides of the jar, and this condition makes it difficult 
to get a proper sample for testing. This daily mixing 



METHODS OF SAMPLING MILK 3I 

also insures the complete solution and distribution of 
the preservative through the milk, which is an es- 
sential condition of success in keeping samples. (5) 
If a composite sample shows any dried or churned 
cream, the sample should be warmed to 105° or 110° F. 
for some minutes and then agitated vigorously be- 
fore drawing the sample for testing. 

AGE OF COMPOSITE SAMPLES WHEN TESTED 

It is advisable to make the fat-test in composite 
samples, when they have been accumulating for a 
week or ten days. In any case the limit should be 
placed at two weeks. The custom practiced by some 
of testing composite samples only once a month should 
be severely condemned. When samples are kept longer 
than two weeks, it is more difficult to get a perfectly 
reliable test for fat. 

PREPARATION OF COMPOSITE SAMPLES FOR 
SAMPLING AND TESTING 

When a composite sample is to be tested, it is 
treated like any other sample previous to taking the 
sample for testing, as has already been described in 
the first part of this chapter on pp. 20-24. 



CHAPTER III 

The Babcock Test — Description of Apparatus 
and Material 

The Babcock test is a method for ascertaining the 
amount of fat in milk and milk products. It was de- 
vised by S. J\L Babcock, Ph.D., chief chemist of the 
Wisconsin Agricultural Experiment Station, and was 
first made public in 1890. There are in use, espe- 
cially in Europe, other tests, which are more or less 
imitations or modifications of the Babcock test, such 
as the Gerber test or acid-butyrometer and DeLaval's 
butyrometer. 

The Babcock test solved the problem of a rapid, ac- 
curate, inexpensive and simple method of testing milk 
and milk products for fat, and it has found extensive 
application in many lines of dairying, as may be shown 
by mention of the following important results coming 
from its use : ( i ) The payment for milk according to 
its fat content has been made practicable. (2) ^lak- 
ers of butter and cheese have been able to detect and 
prevent abnormal losses of fat in the process of man- 
ufacture. (3) It has enabled milk producers to detect 
unprofitable cow^s, thus furnishing an intelligent guide 
in improving their herds. (4) It has done more than 
any other means to stop the watering and skimming of 
milk in connection with creameries and cheese-factor- 
ies. (5) It has been of great service in scientific dairy 
investigations and has, in general, been a source of 
educational inspiration. 

32 



THE BABCOCK TEST 33 

PRINCIPLES AT BASIS OF BABCOCK TEST 

This method is based on the action of two agents: 
(i) the action of strong sulphuric acid upon the con- 
stituents of milk-serum, and (2) the action of cen- 
trifugal force. 

Action of sulphuric acid in Babcock test.— The sul- 
phuric acid used in the Babcock test- performs, at least, 
three functions, which we will consider briefly. 

(r) Action on senim-solids of milk. — Strong sul- 
phuric acid acts chemically and physically upon the 
milk-serum solids (casein, sugar, albumin and salts) 
in such a way as to destroy that strong mechanical, ad- 
hesive influence exerted by the milk-serum solids, 
which tends to prevent the fat-globules separating 
from the form of an emulsion. When this influence is 
overcome, the fat-globules are more free to collect in 
a mass. 

(2) Heat furnished by action of sulphuric acid.— 
The action of sulphuric acid upon the water of milk- 
serum and also upon the organic solids of the serum 
generates so much heat that the fat-globules easily lose 
their individuality and run together, a condition favor- 
ing rapid separation of fat from serum. 

(3) Specihc gravity of serum increased by sulphuric 
acid.— The sulphuric acid, being nearly twice as heavy 
as milk, increases the difference in specific gravity be- 
tween the milk-fat and the liquid surrounding it. The 
milk-fat, being much lighter, more readily rises to the 
surface of the heavy liquid. 

Action o£ centrifugal force in Babcock test.— The 
action of the sulphuric acid having released the milk- 
fat largely from the form of an emulsion in the milk- 



34 



MODERN METHODS OF TESTING MILK 



^0 
=-9 

=-6 



serum, the completion of the separa- 
tion of fat is effected by centrifugal 
force. When the bottles containing 
the mixture of milk and acid are 
whirled, the centrifugal force acts 
more strongly upon the heavier por- 
tion, that is, the mixture of acid and 
milk-serum. Hence this heavy mix- 
ture is forced to the outside, which is 
the bottom of the bottle, while the 
much lighter fat is forced to the top. 
A small amount of fat (.i to .2 per 
cent.) remains unseparated under 
usual conditions. 

The following apparatus and ma- 
terial are used in making the test : ( i ) 
Test-bottles, (2) pipette for measur- 
ing milk, (3) acid-measure, (4) tes- 
ter or centrifugal machine, and (5) 
sulphuric acid. 

TEST-BOTTLES 

The usual form of bottle used in 
testing milk is shown in Fig. 7. The 
neck of the bottle is marked with a 
scale so graduated that each small di- 
vision represents .2 per cent, and five 
of these divisions, making one large 
division, represent i per cent., when we use 17.5CC.* 
or 18 grams of milk. The marks extend from o to 10 




FIG. 7 

MILK-TESTING 

BOTTLE 



*cc. is the abbreviation for cubic centimeters (see p. 205). 



THE BABCOCK TEST 



35 



/\ 



17.6 C.C. 



\/ 



per cent. Why do these divisions represent 
exact percentages by weight of fat in milk, 
when no weighing is done in testing milk? 
We use, in testing, 17.5 cc. of milk, which 
is known to weigh almost exactly 18 grams. 
The graduated portion of the neck of the 
test-bottle is made to hold exactly 2 cc. be- 
tween the o and 10 marks. Since i cc. of 
pure milk-fat is known to weigh .9 gram, 
2 cc. of riiilk-fat, the amount required to 
fill the neck between the o and 10 marks, 
weighs 1.8 (.9x2) grams, which amount is 
just 10 per cent, of the 18 grams of milk 
sample used in testing. 

The divisions on the neck of the test-bot- 
tle should be accurate and uniform ; the lines 
should run straight across the neck and not 
obliquely. When the marks and numbers 
become indistinct from use, they can be 
rendered clear by rubbing the scale over 
with the lead of a pencil or with a cloth 
having on it a little printer's ink or black 
paint. When in use, each bottle should be 
numbered or labeled in a distinctive way. 



MILK-MEASURING PIPETTE 



FIG. 8 
PIPETTE 



The form of pipette in common use is 
shown in Fig. 8. Other forms are shown 
in Figs. 9 and 10. The pipette should hold 
17.6 cc. when filled to the mark. Since 
about ,1 cc. of milk will adhere to the in- 



36 



MODERN METHODS OF TESTING MILK 



side, such a pipette will furnish a sample amounting to 
17.5 cc. of milk, which weighs about 18 grams, i cc. 
of milk weighing about 1.03 grams on an average. 
The accuracy of the test, so far as regards the amount 
of sample taken, depends upon the exactness of the pi- 
pette in holding 17.6 cc. The mark on the stem should, 
for convenience, be two inches or more from the up- 
per end of the pipette^ 

MEASURE FOR ACID 

A cylinder of glass, like that shown 
in Fig. II, with a lip to pour from and 
a single mark at 17.5 cc, is the form 
commonly used. Other forms are shown 
in Figs. 12 and 13. These latter forms, 
made so as to hold enough acid for 20 



FIG. 9 
AUTOMATIC PIPETTE 




FIG. ID 

Wagner's pipette 



^ 



l7.Jcfi, 



^ 



Fia II 

ACID-MEASURE 




THE BABCOCK TEST 



Zl 




FIG. 12 

ACID-BURETTE AND STAND 



FIG. 13 
AUTOMATIC BURETl 



or more tests, are probably the most convenient where 
many samples are to be tested at the same time. 

THE CENTRIFUGAL MACHINE, OR TESTER 

The centrifugal machine used in the Babcock test 
is commonly called the Babcock tester. Various forms 
have been devised, varying in size from those adapted 
for a single duplicate test up to the needs of large fac- 
tories. The designs of recent years are much superior 
to the early forms. Some of the different types are 
represented in Figs. 14, 15, 16 and 17. In general 
they all consist of a revolving disc placed in a hori- 
zontal position, and provided with swinging pockets, 





38 



THE BABCOCK TEST 



39 



in which the test-bottles are placed. When at rest, 
the pockets hang down, permitting the bottles to 
stand upright. When the disc is in motion the pock- 
ets swing out, carrying the bottles to a horizontal posi- 
tion, the necks of the bottles being directed in toward 
the center. The testers should be made to carry an even 




FIG. l6 — SMALL HAND-TESTER 



number of bottles. The steam-turbine tester is the 
best form of centrifugal for factory work. It has the 
advantage of maintaining a luiiform rate of speed 
and, in addition, the contents of the bottles are kept 
hot, and hot water is supplied. In some forms, in 
which the exhaust steam is not carried away and in 
which no dampers are provided in the cover, the steam 
testers may heat the fat too high. For use on farms, 
hand-testers are available. It is always necessary that 
the tester should be securely fastened to a firm founda- 
tion and so set that the revolving disc is level. The 



40 



MODERN METHODS OF TESTING MILK 




FIG. 17 — ELECTRIC CENTRIFUGAL MACHINE OF LATEST DESIGN 

Capable of 2,200 revolutions per minute. Made by the Inter- 
national Instrument Co., Cambridge, I\Iass. 



centrifugal should run smoothly, without jar or trem- 
ble, when going at full speed. 

Estimating speed of centrifugal tester. — In order 
to cause separation of the most fat possible, the cen- 
trifugal disc must move at a sufficient speed. The re- 
quired number of revolutions depends upon the diame- 
ter of the disc, to the edgie of which the test bottles are 



THE BABCOCK TEST 4I 

attached. The smaller the 'wheel, the greater must be 
the number of revolutions a minute. 

Farrington and Woll have prepared the following 
table, shownng the necessary number of revolutions for 
different sizes of testers : 

DIAMETER OF No. of revolutions 
WHEEL IN INCHES of disc pct' minute 
10 . 1074 

12 980 

14 909 

16 848 

18 800 

20 759 

22 724 

24 -^ 693 

In the case of steam-turbine testers, they are, or 
should be, made to run at the desired speed under a 
definite head of steam. These testers should always 
be provided with a pressure-gage, and a speed-indi- 
cator is also desirable. 

In the case of hand-testers, the speed can be ascer- 
tained in the following manner: Give the handle one 
full turn and count the number of times a given point 
on the disc goes round. Suppose, for example, that 
the diameter of the disc is i6 inches and that it revolves 
14 times for one turn of the handle. Such a disc ought 
to revolve 848 times per minute according to the pre- 
ceding table. The handle must be turned around as 
many times a minute as 14 is contained in 848 in or- 
der to attain the desired speed, which is found to be 
about 60 times, or once a second. Then, with watch 
in hand, regulate the turning of the handle until it 



42 MODERN METHODS OF TESTING MILK 

is made to turn 60 times a minute. The proper speed 
once attained should be kept up during the testing of 
a sample. The efficiency of whirling can be further 
tested by treating different samples of the same milk 
at different rates of speed, the highest per cent, of 
fat beyond which there is no increase, showing the 
right speed. 

KIND OF ACID USED IN BABCOCK TEST 

The acid used in the Babcock test is commercial sul- 
phuric acid, commonly known as oil of vitriol. It 
should not be quite as strong as the strongest com- 
mercial acid. While the strong acid has a specific 
gravity of about 1.84, the acid used in the test should 
be between 1.82 and 1.83 at 60° F. 

Effect of weak acid. — If the acid is weaker than 
that indicated by specific gravity 1.82, there is danger 
that some of the coagulated casein may not be com- 
pletely redissolved and this, mixing with the fat, 
makes the fat-column in the test-bottle more or less 
pale and cloudy, when it should be clear and usually 
golden yellow in color. In addition, there is apt to 
be a collection of cloudy matter at the foot of .the fat- 
column, obscuring the line of division and making 
sharp reading difficult. The use of more than 17.5 cc. 
of acid not too weak may give good results. 

Effect of too strong acid. — When the acid is too 
much above specific gravity 1.83, the fat-column is 
dark in color. There is a layer of black material be- 
low it, and the amount of fat is difficult to read with 
accuracy. When the acid is too strong, it is possible 
to secure accurate results by using less than 17.5 cc. 



THE BABCOCK TEST 



43 



of acid, the exact quantity being determined by trying 
different amounts of acid, until the fat-cohmm obtained 
is clear and yellow. Strong acid, if allowed to stand 
open to the air, will in time absorb 
enough moisture to reduce it to proper 
strength. By far the best plan is to 
purchase the acid of guaranteed spe- 
cific gravity 1.82 to 1.83, since all 
dairy-supply houses now furnish such 
acid, and then take pains to keep the 
acid in tightly stoppered bottles when 
not in use. 

Testing strength of acid. — The 
strength of sulphuric acid may be con- 
veniently tested by a specially designed 
hydrometer (Fig 18). This instru- 
ment or acidometer is simply allowed 
to float in the sulphuric acid, which 
must be at 60° F., and the specific 
gravity is read from the scale where 
it coincides with the upper surface of 
the liquid, which should be between 
the scale-marks 1.82 and 1.83. No testing strength 
acidometer should be used whose ac- of sulphuric 
curacy is not reliably guaranteed. acid 

Reducing the strength of strong acid. — With the 
aid of an acidometer, it is possible to purchase strong 
sulphuric acid and dilute it to proper strength. This 
is not advised for the average worker. When this is 
done, extreme caution must be used in diluting the 
acid. Never pour- water into strong sulphuric acid, 
but always add the acid to the water. The amount of 



FIG. 18 
HYDROMETER FOR 



44 MODERN METHODS OF TESTING MILK 

dilution depends upon the strength of the acid used. 
One should start with a small dilution and increase 
gradually until the specific gravity of the acid becomes 
1.82 to 1.83. After diluting the acid with water, the 
mixture becomes hot, and it is necessary to allow it 
to cool to 60° F. before testing with the acidometer. 

Useful indications regarding strength of acid. — 
After one has acquired some skill in making the Bab- 
cock test, one can readily tell whether the acid is too 
strong or too weak from its action when mixed with 
milk in the test-bottle. One bases his judgment on 
the rapidity with which the milk-casein is coagulated 
and redissolved, and also upon the quickness with 
which, and the degree to which, the mixture of acid 
and milk turns dark. 

Keeping acid from air. — The acid should be kept 
in tightly stoppered bottles, because, if exposed to air, 
it absorbs moisture and becomes too weak. The stop- 
per should be glass, since a common cork stopper is 
soon destroyed by the acid, and even rubber is not 
long satisfactory. 

Care in handling sulphuric acid. — Strong sulphuric 
acid is extremely corrosive and is dangerous to han- 
dle except with care. In contact with articles like 
clothing or leather, it quickly ruins them, while on 
the skin it causes serious burns in a short time. If 
sulphuric acid gets upon one's skin, it should be imme- 
diately and thoroughly washed with an abundance of 
water, and this may be followed by washing with di- 
lute ammonia or sodium carbonate. In case acid gets 
on the clothing, treat it first with abundance of water 
and then with ammonia. Red discoloration on cloth- 



THE BABCOCK TEST 45 

ing caused by acid may be remedied by treatment with 
ammonia, if not too long delayed. Acid on tables, 
floors, etc., may be neutralized by treatment with 
washing soda or other alkali. 

METHODS OF TESTING ACCURACY OF 
APPARATUS 

The correctness of the graduation of the glassware 
used in the Babcock test is a fundamental condition of 
accuracy in the results obtained. In some states all 
graduated glassware used in the Babcock test must 
be tested by the state and found correct before its use 
is permitted in commercial operations. Reliable deal- 
ers guarantee the accuracy of their glassware, and it 
is found to be much more reliable than formerly. How- 
ever, it is a safe precaution always to test new appa- 
ratus before using it. Testing graduated glassware 
is known technically as calibration. 

Testing or calibrating milk-bottles. — Test-bottles 
which show a variation, above or below, of more than 
one division, or .2 per cent., in the 10 per cent, scale, 
should not be used. The different methods of test- 
ing will now be considered. 

(i) Testing zvith special bottle-tester. — The quick- 
est method of testing the accuracy of the scale of a 
test-bottle is to use a special device, which is essentially 
a simple brass plunger (Fig. 19). This instrument is 
divided into two equal portions, each part being made 
of such a size as to displace exactly one cubic centi- 
meter of liquid. This bottle-tester is used as follows : 
The test-bottle is filled to the zero mark with milk, or 
one may use water or, better, wood alcohol, imparting 



46 



MODERN METHODS OF TESTING MILK 



color to the water or alcohol by adding some black 

aniline or carmine ink. Fill the bottle nearly to the 

zero mark and then finish with a pipette or dropper, 

>^ adding a drop at a time just 

to the mark. Any drops of 

liquid adhering to the inside 

Ou 'f walls of the neck must be re- 

^ '^ moved, using conveniently a 

strip of blotting or filter pa- 
per. The tester is then slowly 
lowered into the neck of the 
test-bottle until the liquid rises 
half way between the two 
sections of the instrument, 
when the upper surface of 
the liquid should be at the 5 
per cent, mark (Fig 20), if 
the scale is correct to this 
point. If the surface of the 
liquid is above or below the 
5 per cent, mark, then the 
scale is incorrect to that ex- 
tent. After the accuracy of 
the 5 per cent, mark is tested, 
the instrument is then lowered 
into the bottle until the liquid 
rises about one-eighth of an 
inch above the top of the up- 
per section of the tester. If 
the upper surface of the liquid is level with the 10 
per cent, mark, the graduation is correct at that point. 
The graduation of the scale is regarded as correct, if 



M Shi 



'-I 



FIG. 19 



FIG. 20 
TESTING 
MILK-BOTTLE ACCURACY OF 
TESTER MILK-BOTTLE 



THE BABCOCK TEST 47 

the tester shows the. 5 and 10 per cent, marks to be 
correct. 

In explanation of the use of this form of bottle-tes- 
ter, it is to be remembered that the neck of the milk- 
bottle is so graduated as to hold 2 cc. between the o 
and 10 marks ; hence, the volume between the o and 
5 marks should be i cc, and that between the 5 and 
10 marks should be also i cc. The brass plunger is 
so made that each section displaces, or forces up into 
the neck, i cc. of liquid, the wdiole instrument displac- 
ing 2 cc. This tester therefore gives two tests of the 
scale, one at the 5 per cent, mark and the other at 
the 10 mark. 

Some of these instruments are made to test the 4 
and 8 per cent, points, so that with two testers, one 
can, if desired, test the accuracy of the scale at the 
4, 5, 8 and 10 points. There are also testers of the 
same form made for cream-bottles. 

In using this bottle-tester, the following precautions 
are to be observed : 

(i) Have the upper surface of the liquid exactly 
on a level with the zero mark in the neck of the test- 
bottle before putting the tester in. 

(2) Clean the inside walls of the neck of the bot- 
tle from adhering liquid before testing. 

(3) No air-bubbles should be allowed to adhere to 
the tester when it is below the liquid. 

(4) The tester should be dry each time before using. 
(2) Testing zvith mercury. — From an accurately 

graduated burette (Fig. 21), measure 2 cc. of clean 
mercury into the bottle to be tested. Then push down 
into the neck of the bottle as far as the top line of 



48 



MODERN METHODS OF TESTING MILK 



y 1 % § f » m 



graduation a close-fitting cork or plug, cut off square 
at the lower end. Turn the bottle upside down, caus- 
ing the mercury to run into the neck. The mercury 
just fills the space in the neck between the o and lo 
mark, if the graduation is accurate. The same 
mercury can be used in the same way in test- 
ing one bottle after another by 
transferring all the mercury 
from one bottle to another, which 
may be conveniently done by 
slipping a piece of elastic rub- 
i ber tubing over the ends of the 

necks of the two bottles. In 
using the same mercury for test- 
ing one bottle after another, no 
mercury must be lost in trans- 
h^ —-jdmktti^ ferring, and none must be left 
w^ ^^^^ ^^fi in the bottle last tested. The 
inside walls of the test-bottle 
must be dry and clean in order 
to prevent any mercury adhering. 

(3) Testing zvith zvater. — The bottle to be tested 
is filled with water, slightl}^ colored wnth carmine ink, 
or otherwise, up to the zero mark. The coloring of 
the water makes easier the reading of the height of 
the liquid. Any water adhering to the inside of the 
neck is removed by a strip of blotting or filter paper. 
Then one runs into the test-bottle 2 cc. of colored water 
from a burette or pipette, graduated to twentieths of 
a cubic centimeter. The upper surface of the liquid 
should be on a level with the 10 per cent, mark if the 
scale is correct. Any part of the scale can be similarly 



FIG. 21 
BURETTE AND SUPPORT 



THE BABCOCK TEST 49 

tested, remembering- that each per cent, on the scale 
should contain just .2 cc. of liquid. 

Testing accuracy of pipette. — When many pipettes 
are to be tested, one runs into one pipette from an 
accurately graduated burette (Fig. 21), 17.6 cc. of 
mercury, closing the lower end of the pipette. The 
mercury should fill the pipette just to the 17.6 cc. 
mark, if the mark is correct. The same mercury can 
be transferred to other pipettes in succession. Care 
must be taken to have the pipettes clean and dry in- 
side and that all the mercury is transferred without 
loss. 

When only one or a few pipettes need testing, wa- 
ter can be used, running from a burette into each pi- 
pette 17.6 cc. of water, which should just fill the 
pipette to the mark, if accurate. 

Testing accuracy of acid measure. — Ordinarily the 
acid measure does not need testing, since a little varia- 
tion does not afifect the results. When desired, it can 
be tested by running in water or milk from a 17.6 cc. 
pipette, known to be accurate. 

KEEPING GLASSWARE CLEAN 

It is very important that the test-bottles and the 
pipettes used in the Babcock test should be kept as 
clean as possible from fat adhering to the inside sur- 
face. Unless a special effort is made, the bottles 
quickly become covered inside with a film of fat, 
which may be sufficient to increase appreciably the 
results obtained when the bottles are used in testing. 
The bottles should be kept entirely free from any fat- 



50 



MODERN METHODS OF TESTING MILK 



film and the wall should be clear and bright. This 
can be accomplished without serious trouble. 

As soon as a test is completed and the amount of 
fat read, the test-bottle, while still 
warm, should be emptied. This 
may easily be done by having a 
large earthenware jar or crock, 
covered with a board (Fig. 22), 
in which are several holes large 
enough to admit easily the necks 
FIG. 22— WASTE-JAR of tcst-bottlcs. The bottle is in- 

FOR EMPTYING ^1^1 1 j ^1 t, 

TEST-BOTTLES vcrtcd, thc ucck run down through 
one of these holes, and at the 
same time the bottle is shaken up and down in 
order to remove the white calcium sulphate de- 
posited on the bottom of the bottle during the test. 
Then, when one is ready to clean up all the bottles 
that have been used, each one is rinsed with 8 or lo 





FIG. 23 — TEST-BOTTLE KINSER 



THE BABCOCK TEST 



51 





.-P 




^^P 



FIG. 24 — TEST-BOTTLE DRAINING RACK 

cc. of a solution, consisting of one ounce of potassium 
bichromate dissolved in one pint of sulphuric acid. 

Then a test-bottle brush 
is run once up and down 
the neck of each bottle, 
and finally each is well 
rinsed with hot water. 
There are available 
several devices which 
may be found convenient 
and time-saving where 
many bottles are used 
daily. Among these de- 
vices may be mentioned 
a bottle-rinser (Fig. 23), 
a drain-rack (Fig. 24), 
and a bottle- 
washer (Figs. 
2^a, h, and c), 
described by 
Farrington 
(Bulletin 129, 
Wis. Agr. Exp. 
Station, pp. 22- 
24). 




FIG. 25a — BOTTLE-HOLDERj EMPTY 





52 



CHAPTER IV 



Method of Operating the Babcock Test 

In describing the method of operating the Babcock 
test, when determining the amount of fat in milk, 
special attention will be called at each step to such 
difficulties as may occur, and emphasis will be placed 
upon such precautions as experience has shown to be 
necessary in order to obtain accurate results. 

In brief outline, the different steps may be . stated 
as follows : 

I Mix thoroughly sample of milk, which is at 60° to 
70° F. 

2. Quickly fill pipette to mark with milk. 

3. Run milk into test-bottle. 

4. Fill acid-measure to mark with acid and pour into 

test-bottle. 

5. (i) Mix milk and acid thoroughly by rotary motion; 

(2) let stand 2 to 5 minutes; and (3) mix again. 

6. Put test-bottles in tester (centrifuge) and whirl 4 or 

5 minutes at proper speed. 

7. (i) Add fairly hot water up to neck of bottles; (2) 

whirl one minute; (3) add hot water to 8 or 9 per 
cent, mark; and (4) whirl one minute. 

8. Read results at temperature of about 130° F. 

PREPARING SAMPLES OF MILK FOR TESTING 

The milk, which should be at a temperature of 60° 
to 70° P., is thoroughly mixed by pouring from one 
vessel to another two or three times, at least, imme- 

53 



54 MODERN METHODS OF TESTING MILK 

diately before taking the sample for testing. The spe- 
cial methods of preparing milk for sampling under 
various conditions are fully considered in Chap. II, 
p. 20. The fat must be evenly distributed through 
the milk just before sampling. 

Every sample of milk should always be tested in 
duplicate, that is, two tests should be made at the 
same time. This insures greater accuracy. If the 
results of the duplicate test do not agree, there is an 
error somewhere and the work must be repeated. Also, 
in case one test is lost and another sample can not be 
obtained, the remaining test can be used, and the whole 
work will not be lost. 

TAKING SAMPLES OF MILK WITH PIPETTE 

The measuring pipette (Fig. 8, p. 35), is filled at 
once after the thorough mixing of ^ the milk. This is 
done by placing the lower end of the pipette well down 
in the milk and sucking up the milk until it reaches 
a point in the pipette somewhat above the mark around 
its upper stem. Then the forefinger, zvhich must be 
dry, is quickly placed over the upper end of the pi- 
pette before the milk runs down below the mark. By 
lightening the pressure of the finger on the end of 
the pipette, the milk is allowed to flow out slowly un- 
til its upper surface just reaches the mark on the 
stem. Some practice is necessary before one can eas- 
ily and rapidly manipulate the pipette with accuracy. 

The pipette must be kept very clean. When sam- 
ples of several different milks are to be drawn in suc- 
cession, the pipette may be satisfactorily rinsed by 



THE BABCOCK TEST 



55 



drawing it full of the milk 
next to be sampled, this por- 
tion being thrown away. 

TRANSFERRING SAMPLE 

OF MILK FROM PIPETTE 

TO TEST-BOTTLE 

Having filled the pipette 
just to the 17.6 CO. mark, one 
holds the pipette obliquely to 
the bottle, placing the point 
of its lower end within the 
neck and agaiiist the side of 
the neck of the test-bottle. 
The right way of holding the 
pipette is shown in the Fig. 
26. By loosening the finger 
at the upper end of the pipette, 
one allows the milk to flow "^ 
slowly down the inside of the V 
neck. The small portion of a 
milk adhering to the inside of ^ 
the pipette is nearly all carried 
into the bottle by blowing 
through the pipette several 
times before removing it from 
the neck of the bottle. Not 
a drop of the milk should be fig. 26— correct way of 
allowed to spill outside the holding pipette and 
bottle in transferring from bottle 

the pipette. 

It is not intended to remove every trace of milk 
from the pipette into the bottle, since allowance for 




56 



MODERN METHODS OF TESTING MILK 



what remains is made in the 
construction of the pipette. 
Special experiments having 
sliown that .i cc. of milk will 
remain adhering to the inside, 
the pipette is made to hold 
17.6 cc. to the mark, but is 
expected to deliver into the 
bottle only 17.5 cc, the exact 
amount required for the test. 
In delivering the milk, the 
pipette must never be held 
perpendicularly in a line with 
the neck of the test-bottle, 
running the milk straight 
down as shown in Fig. 26a, 
since the narrow neck may 
easily choke up. with milk and 
run over the top. 

MEASURING AND ADDING 
ACID 

When the samples of milk 
are in the test-bottles, the acid- 
measure (Fig. II, p. 36), is 
filled to the 17.5 cc. mark and 
the acid (see p. 42) is poured 
FIG. 26a— WRONG WAY OF iuto thc tcst-bottlc. The acid 
HOLDING PIPETTE AND sliould bc at a tcmpcrature of 
BOTTLE 60° to 70° F. Much carc 

must be exercised in pouring 
the acid into the test-bottle containing the milk. The 
test-bottle is held in an inclined position, so that the 




THE BABCOCK TEST 57 

acid will follow the inside wall down to the bottom, 
and the pouring should be slow and steady. Thus 
handled, the acid, being much heavier than the milk, 
forms a layer by itself at the bottom of the bottle, 
while the milk forms a separate layer by itself on top 
of the acid. While pouring in the acid, it is well to 
turn the test-bottle around slowly so the acid may in 
turn come in contact with different portions of the 
inside walls of the neck and wash down any adhering 
milk. Unless this is done, some milk may remain on 
the wall of the neck, in which case it will not be prop- 
erly acted on by the acid, and the fat-column will con- 
tain particles of undissolved casein. 

If one attempts to pour the acid straight down the 
neck of the bottle, two difficulties are liable to occur: 
(i) The neck may easily choke up and the acid over- 
flow on the operator's hands. (2) The acid may drop 
into and partially mix with the milk, in which case 
black particles may appear on the upper surface of the 
acid layer and later, mixing in the fat-column, may 
interfere with accurate reading of the results. 

Temperature of milk and acid. — It is directed to 
have the milk and acid at a temperature of 60° to 
70° F. before they are placed in the test-bottle. There 
are good reasons for this precaution. If the milk or 
acid is decidedly cold, as may easily happen in cold 
weather, the action of the acid may not be vigorous 
enough to redissolve completely the coagulated casein, 
thus producing white specks or a cloudy appearance 
in and below the fat-column at the end of the test. 
On the other hand, if the milk or acid is at too high 
a temperature, as may easily happen in hot weather, 



58 MODERN METHODS OF TESTING MILK 

the action of the acid is much the same as if it were 
too strong, producing dark-colored specks or a dark- 
ened appearance in and below the fat-column. Ex- 
perience shows that when the milk and acid are at a 
temperature between 60° and 70° F., there is no dan- 
ger of too slight or too strong action of acid. More 
acid can be used at lower temperatures and less at 
higher temperatures with satisfactory results, but this 
involves experimenting; the best way will be to use 
the regular amount of acid and regulate the tempera- 
ture of the milk and acid. 

MIXING MILK AND ACID IN TEST-BOTTLE 

When the measured amount of acid has been placed 
in the test-bottle, the acid and milk should be thor- 
oughly mixed. This is best done by giving the bot- 
tle a rotary motion, with gentle shaking, until the 
whole mass becomes liquid and free from solid parti- 
cles of casein. Much motion up and down should be 
avoided, since milk might be thrown up into the neck 
of the bottle beyond reach of the acid, in which case 
coagulated casein would contaminate the fat-column 
and impair the results. 

When the acid and milk first mix, the casein is 
coagulated in a somewhat solid mass, which gradu- 
ally redissolves as the mixing becomes complete. The 
mixing, once begun, should continue until the casein 
appears to be redissolved. If the operation of mixing 
milk and acid is incomplete or is interrupted, black 
particles may appear in the fat-column at the end of 
the test. 

It is a wise precaution to allow the bottle to stand 



THE BABCOCK TEST 59 

2 to 5 minutes after the mixing appears complete and 
then to agitate a second time with rotary motion just 
before placing in the tester. 

The action of the sulphuric acid upon the water and 
organic solids of the milk produces a marked degree 
of heat, as soon as the acid and milk begin to mix. 
The color of the solution becomes yellow at first and 
then passes through varying darker shades of yellow 
to violet, brown and finally dark-brown, if the acid is 
of the right strength. (See p. 42.) The coloration is due 
to the action of the acid upon the milk-sugar and milk- 
casein. Too strong acid produces a dense black color. 
In samples of milk containing too much bichromate of 
potash, the color becomes greenish black. 

Samples of milk that have been preserved for some 
time with bichromate or formalin, especially when the 
preservative is used in larger than usual amounts, re- 
quire more time and agitation to redissolve the coag- 
ulated casein than do ordinary samples, since these 
preservatives harden the coagulated casein. ( See p. 29) . 

WHIRLING THE TEST-BOTTLES 

The test-bottles containing the mixture of milk and 
acid, after being agitated a second time as stated above, 
are placed in the centrifugal tester (p. 37), and 
whirled. This is better done soon after the milk and 
acid are mixed, but it may be delayed without harm 
for 24 hours, in which case, however, the bottles 
should be placed in water at 160° to 180° F. for 15 
or 20 minutes before whirling. 

An even number of bottles should be whirled at the 
same time and they should be placed about the disc 



6o MODERN METHODS OF TESTING MILK 

in pairs opposite to each other, so that the equiHbrium 
of the tester will not be disturbed. When all the sam- 
ples to be tested are placed in the tester, the cover 
is placed on the jacket and the machine turned for 4 
or 5 minutes at proper speed, 600 to 1,200 revolutions 
per minute, according to the diameter of the centri- 
fugal disc. (p. 40.) 

The whirling brings the fat to the top of the mix- 
ture in the test-bottle. The whirling of the bottles 
should never be done without having the cover on the 
jacket, for two reasons: (i) The cover prevents the 
cooling of the fat in the test-bottles during whirling, 
and (2) the operator is protected from injury in case 
a bottle should break and scatter its contents while 
being whirled. 

In the case of hand-testers, it may be necessary to 
put hot water in the jacket in cold weather in order 
to keep the bottles warm enough. 

ADDING HOT WATER TO THE TEST-BOTTLES 

When the bottles haA^e been whirled 4 or 5 minutes, 
moderately hot water is added to each bottle until the 
contents come to the lower end of the neck. The 
water may be added with a pipette or by means of 
any convenient arrangement. The cover of the ma- 
chine is replaced and the bottles are whirled at full 
speed for one minute. Hot water is again added to 
the bottles until the fat, which is lighter than the rest 
of the liquid, rises in the neck to the 8 or 9 per cent 
mark. One must be careful never to run the water 
above the 10 per cent. mark. The whirling is then re- 
peated for one minute at full speed. 



THE BABCOCK TEST 6l 

Three points deserve attention in this connection : 
(i) The temperature of the water added, (2) the 
kind of water used and (3) the number of times water 
is added. 

(i) The temperature of the water added should be 
above 120° F. The aim in general should be to have 
the temperature of the fat at the close of whirling at 
130° or 140° F., and the temperature of the water 
added should have reference to this fact. However, 
any efifect of too hot or too cold water can be remedied 
after the final whirling. by adjusting the temperature 
as needed. 

(2) Clean, pure, distilled water is the best form to 
use and, next, soft rain water. Hard water may seri- 
ously affect the results. Objections to hard water 
may in most cases be overcome by thorough boiling 
or by previous treatment with a few drops of sul- 
phuric acid. 

(3) Some operators add the hot water only once, 
filling the bottle to near the top of the neck immedi- 
ately after the first whirling. The advantage of ad- 
ding the water in two portions is that the fat is washed 
free from adhering impurities, since the fat-column is 
often mixed with various particles which render the 
reading uncertain and frequently too high. 

READING RESULTS IN PERCENTAGE OF FAT 

After the last whirling is completed, the test-bottles 
are removed from the tester, one at a time, in order 
to read the results of the test. To ascertain the 
amount of fat, hold the test-bottle upright, having the 
graduated scale of the neck of the bottle on a level 



62 MODERN METHODS OF TESTING MILK 

with the eye. Notice the divisions marking the high- 
est and lowest hmits of the fat-column. The differ- 
ence between them gives directly the per cent, of fat 
in the milk tested. The readings can be made accu- 
rately to one-half of a division, that is, to one-tenth of 
one per cent. Some test-bottles are provided with a 
regulator which moves the bottom of the fat-column 
to a level with the nearest numbered mark. 

In connection with the measuring of the fat-column, 
the following points deserve attention : ( i ) Using divi- 
ders to assist in reading, (2) the temperature of the 
fat-column, (3) the upper and lower limits of the 
fat-column, (4) the correct appearance of the fat- 
column, (5) defects in appearance of the fat-column. 

(i) If one uses test-bottles not provided with a reg- 
ulator for adjusting the level of the fat-column, the 
reading of the percentage of fat on the scale may be 
made with less liability of error by measuring the 
length of the fat-column with a pair of dividers, one 
point of which is placed at the bottom and the other 
at the upper limit of the fat-column. The dividers 
are then removed and one point is placed on tte zero 
mark of the scale on the bottle used, when the other 
point v/ill be at the exact per cent, of fat in the milk 
tested. 

(2) The temperature of the fat, when it is read or 
measured, should be above 120° F. and not above 
140° F., preferably about 130° F. This will insure 
sharply defined upper and lower limits of the fat-col- 
umn. In case the contents of the bottles are below 
120° F., the bottles should be placed for 15 or 20 min-"» 
utes in water that has a temperature of 130° to 140° F., 



THE BABCOCK TEST 



63 



before the reading is 'made. This usually needs to be 
done in cold weather, when hand-testers are used, 
especially if no hot water has been placed in the jacket 
during the whirling. If the fat is above 150° F., it 
should be allowed to cool to 140° F. or below before 
reading the results. Too high temperatures give too 
high results, because the fat-column expands. 

(3) The line of division between the fat-column and 
the liquid beneath is nearly a straight line when the 
testing is properly done, and one need have no doubt 
about the reading of the scale at this point. But the 
upper surface of the fat-column is 
concave instead of straight, which 
may cause some uncertainty as to the 
exact point at which the reading 
should be made on the scale. The 
correct reading is taken at the line 
where the upper surface of the fat- 
column meets the sides of the neck, 
the very highest point at which the 
fat-column is seen. The reading 
should not be made from the dark 
line or meniscus lower down, which 
is caused by the refraction of the 
curved surface. The points at which 
the readings should be made are shown 
in Fig. 27, indicated as A and B. 
Results read this way agree with those 
obtained by gravimetric analysis. The 
objection may be raised that we get too high results 
by reading from the extreme top points of the fat- 
column, just as if the upper surface were straight at 



A 



FIG. 27 
MEASURING 
FAT-COLUMN 



04 MODERN METHODS OF TESTING MILK 

these points instead of concave. While there is such 
an apparent error, the excessive reading thus caused 
is only enough to make up for the loss of fat which 
can not be separated from the rest of the liquid by 
centrifugal force and brought into the fat-column. The 
amount of fat thus left in the mixture of milk-serum 
and acid is ordinarily about .2 per cent, and this is 
about the amount of excess obtained by the approved 
method of reading the upper limit of the fat-column. 

(4) The fat appearing in the neck of the test-bot- 
tle at the end of a successful test is of a clear, yellow 
color, and the line of division between its lower limit 
and the acid solution beneath it is sharply distinct. 
However, the fat is apt to be light-colored in the case 
of milk from cows far along in lactation. 

(5) The fat-column may show certain defects, if 
the conditions of the test have not been properly car- 
ried out, among which are (a) black particles below 
or above or in the fat-column, or a darkened appear- 
ance of the whole column of fat; (b) white particles 
below or above or in the fat-column, or a cloudy ap- 
pearance of the whole column; and (c) bubbles on 
the surface. 

(a) Black particles in the neck of the test-bottle at 
the end of the test, or a darkened appearance of the 
fat itself, are due to one or more of the following 
causes: (i) Too strong acid (above 1.83 specific grav- 
ity), (2) too much acid (more than 18 cc), (3) too 
high temperature of the milk or acid (over 75° F.), 
(4) allowing milk and acid to stand in test-bottle too 
long before mixing, (5) allowing the acid to drop 



THE BACCOCK TEST 65 

through the milk when poured into the test-bottle, 
(6) interrupting the mixing of the milk and acid af- 
ter beginning and before completion. 

(b) White particles of undissolved casein below or 
above or in the fat-column, or a cloudy appearance of 
the fat, are due to one or more of the following causes : 
(i) Too weak acid (below 1.82 specific gravity), (2) 
insufficient amount of acid (less than 17 cc), (3) too 
low temperature of milk or acid (below 60° F.), (4) 
incomplete mixing of milk and acid, (5) insufficient 
speed of tester. 

Sometimes when the fat is not clear, good results 
may be obtained by allowing the bottles to cool enough 
for the fat to harden some, and then warming in wa- 
ter at 140° F. before reading. 

(c) Bubbles of gas, appearing as foam on the top 
of the fat-column, are generally due to the use in the 
test-bottle of hard water containing carbonates. This 
condition may be prevented by adding to the water, 
previous to use, a few drops of sulphuric acid. When 
the foam appears and interferes with the reading, a 
few drops of alcohol are put on the top of the fat-col- 
umn and the reading is at once made. The alcohol 
causes the bubbles to disappe.ar and produces a sharp 
line of division between the fat and alcohol. If the 
alcohol is allowed to be in contact with the fat for 
some time before the reading is made, the alcohol and 
fat mix and increase the height of the fat-column, thus 
producing misleading results. 



66 MODERN METHODS OF TESTING MILK 

OUTLINE STATEMENT OF SOME SPECIAL 
PRECAUTIONS 

1. Always make tests in duplicate. 

2. Make sure that the sample is a representative one. 
3.' Have the temperature of the milk and acid at 

60° to 70° F. before putting in test-bottle. 

4. Use only acid of right strength. 

5. Mix milk and acid thoroughly as soon as acid 
is added. 

6. Mix a second time after a short interval. 

7. Make sure that the tester runs at right speed 
and does not jar. 

8. Use only clean, soft water in filling bottles. 

9. Read bottles before they cool and at about 130° F. 

10. To insure accuracy, read each test twice. 

SOME MODIFICATIONS OF THE BABCOCK TEST 

One frequently sees references in dairy literature 
to other forms of tests for milk. As a matter of in- 
formation, we will notice a few of the modifications of 
the Babcock test together with other forms that are 
in use, giving good results. 

The Russian Test. — This is a modification of the 
Babcock test, differing mainly in respect to some of 
the mechanical details. A special automatic pipette is 
used (Fig. 28), a special form of test-bottle (Fig. 28a), 
the neck being separate from the rest of the bottle, and 
also a special form of acid-measure. The pipette and 
acid-measure are one-half the usual size. The milk and 
acid are run into the bottle very easily, and the bot- 
tles are filled with hot water automatically while the 
machine is in motion, the tester also being of a special 
form. 



THE BABCOCK TEST 



67 



The Gerber Butyrometer. — Special forms of tes- 
ter, test-bottle, etc., are used. The test uses 11 cc. of 
milk, 10 cc. of sulphuric acid (1.825 specific gravity), 



\ 




U 

FIG. 28 

AUTOMATIC "Russian' 



PIPETTE 



FIG. 28a 
'RUSSIAN^'' TEST-BOTTLE 



and I cc. of amyl alcohol. The operations are carried 
out about the same as in the Babcock test. 

The "Sinacid" (no acid) Test. — The distinctive fea- 
ture of this test is that, in place of sulphuric acid, it 
uses a patented mixture, consisting of sodium phosphate 
and citrate, which, unlike sulphuric acid, is entirely free 
from any dangerous properties ; it uses also a colored 



68 MODERN METHODS OF TESTING MILK 

alcoholic solution. After mixing the "sinacid" liquid 
with the milk, the mixture is heated to 200° F. for 5 
minutes before being whirled in the tester. The re- 
sults do not always appear to agree closely with those 
given by other tests, according to the reports of some 
operators. There is, moreover, some natural preju- 
dice against using a process, any part of which is 
patented. 

Gerber's "Sal" Test. — Gerber has just published a 
method in which no acid is used. The full details are 
not given, since the method is to be patented. Good 
results are reported. 



CHAPTER V 

Method of Testing Cream by the Babcock Test 

The Babcock test can be used in ascertaining the 
amount of fat in cream, but certain precautions and 
modifications are necessary to insure correct results. 
A special form of test-bottle is generally used. Spe- 
cial pains must be taken in sampling cream. For 
strictly accurate work, the cream sample must be 
weighed for testing. 

USE OF MILK TEST-BOTTLES IN TESTING 
CREAM 

Test-bottles used in testing milk can be used in 
testing cream only under special conditions. Cream 
containing over lo per cent, of fat will fill the neck 
of the test-bottle too full for measurement, when we 
take 1 8 grams (about 17.5 cc.) to test. This difficulty 
may be overcome in two ways : ( i ) By using a sample 
of cream less than 18 grams, and (2) by dividing an 
i8-grani sample in roughly equal parts between two or 
more bottles, according to its richness in fat. In the 
former case the per cent, of fat read is increased by 
a correction to be considered later. In the second case, 
the tests are made as in case of milk and the per- 
centages found in the different bottles are added, the 
sum being the per cent, of fat in the cream tested. The 
volume of cream in each test-bottle is always made up 

69 



70 



MODERN METHODS OF TESTING MILK 



to about 17.5 cc. by adding water to 
the cream and mixing before adding 

acid. 

SPECIAL CREAM-TESTING 
BOTTLES 

To test in one bottle an 18-gram 
sample of cream containing over 10 
per cent, of fat, the neck must be 
made to hold more than the neck of 
a milk-bottle, that is, more than 2 cc. 
This additional space must be ob- 
tained (i) by using a neck of larger 
diameter, keeping the length the same 
as in the milk-bottle or (2) by mak- 
ing the neck longer, keeping the diam- 
eter the same. There is this objection 
to making the necks of test-bottles too 
large in diameter, that the divisions 
on the scale come nearer together 
and the reading of the results is less 
accurate. If the neck is made long 
enough to allow as fine graduation 
as in the milk-testing bottles, then 
the bottles are too long to use in an 
ordinary tester. 

Bulb-necked cream-bottle. — Both 
of the difficulties mentioned above are 
overcome by having a bulb made in 
the neck of the bottle (Fig. 29). In 
this cream-testing bottle the gradua- 
tion is as fine as in the milk-testing 
bottles, the smallest division repre- 
senting .2 per cent., and the scale ex- 



— 5 



FIG. 29 

BULB-NECKED 
CREAM -BOTTLE 



TESTING CREAM BY THE BABCOCK TEST 



71 



tends from o to 25 per cent. Hence, in these bottles 
we can use 18 grams of cream, provided the cream 
does not contain over 25 per cent, of fat, while, with 
cream testing over 25 and up to 50 per cent., a 9- 
gram sample can be used for the test. In using this 
form of bottle, care must be observed 
v^hen water is added near the close 
of the test. Neither the lower nor the 
upper surface of the fat-column must 
be allowed to come in the bulb, since, 
obviously, it is impossible then to read 
the results. This style of bottle is also 
made with a scale measuring 50 per 
cent., the smallest divisions being .25 
per cent. 

Straight-necked cream-bottles. — 
The other varieties of cream-testing 
bottles are straight-necked, varying in 
respect to (i) diameter, (2) length 
of neck, and (3) fineness of gradua- 
tion. These vary in length from the 
ordinary size to 9 and 10 inches, the 
longer sizes requiring special testers. 
In capacity, the necks vary from 6 to 
20 cc, which is equivalent to 30 to 100 per cent., when 
an 18-gram sample of cream is used. In fineness of 
graduation, the smallest divisions vary in different bot- 
tles from .2 to I per cent. One type of straight-necked 
bottle is shown in Fig. 30. For strictly accurate work, 
bottles graduated to .2 per cent, should be used; and 
the use of bottles whose finest division is more than 
.5 per cent, should be condemned, except for rough 
work. 




FIG. 30 

STRAIGHT-NECKED 
CREAM-BOTTLE 



72 



MODERN METHODS OF TESTING MILK 



CREAM-TESTING SCALES 

For weighing samples of 
cream, a set of accurate 
scales is required. Differ- 
ent forms are illustrated in 
Figs. 31 and 32. Scales 
with agate bearings are 
much preferable to other 
forms, since the agate bear- 
ings do not rust. Torsion balances and those with 

o 

steel bearings are liable to rust when kept in damp 




FIG. 31 
CREAM-TESTING SCALES 




FIG. 32 — CREAM-TESTING SCALES 

places, and this in time makes them unreliable for 
accurate work. The scales should be kept in perfect 
condition and tested for accuracy from time to time. 



METHOD OF SAMPLING CREAM 

Cream, from which the test sample is to be taken, 
whether for part of a composite sample or for direct 
testing, must be made as uniform as possible through- 
out its mass. The best method of sampling any but 



TESTING CREAM BY THE BABCOCK TEST 73 

small amounts of cream is by means of a sampling- 
tube (Fig. 5, p. 27), which must be cleaned for each 
sample before using. Frozen cream must be thawed 
and mixed before sampling. Large lots of dried 
cream or partially churned cream can not be sam- 
pled with complete accuracy. Cream adhering to 
the outside of the sampler should not be allowed to 
go into the test sample. 

METHOD OF KEEPING CREAM SAMPLES 

In keeping composite samples of cream, the same 
precautions are to be observed as in the case of milk 
(p. 30). With thick cream special effort may be 
needed to cause the preservative, especially potassium 
bichromate, to dissolve and be distributed through 
the sample. This may be done b}^ warming the jars 
and mixing the cream carefully by a gentle rotary mo- 
tion. 

PREPARATION OF SAMPLES FOR TEST 

Before taking from the cream sample the amount 
to be used in the test, the cream must have its fat 
evenly distributed. To accomplish this, the cream is 
heated to 105° or 110° F. until it is quite fluid. As 
recommended by Flills (Bulletin 100, Vermont Exp. 
Sta., p. 5), the cream is passed through a small sieve 
(Fig. 33), such as is commonly used in kitchens. Any 
remaining lumps found in the sieve are rubbed through 
the meshes by the finger, after which the cream is 
thoroughly mixed by pouring from one cup to another. 
The sample is then quickly taken for testing. 




74 MODERN METHODS OF TESTING MILK 

WHY USE OF PIPETTE IS INACCURATE FOR 
CREAM 

The use of a pipette in measuring cream samples 
is inaccurate for the following reasons : ( i ) More fat 
adheres to the inside of a pipette than in case of 
milk, the error increasing with the thickness of cream. 
(2) The weight of cream decreases as the per cent, 
of fat in cream increases, since milk-fat is lighter 

than the other 
constituents 
of cream. The 
scale of the test-bottle is 
based on the use of 18 
grams of material, but the 
amount of cream that oc- 
FiG- 33 cupies the volume filled by 

CREAM-SAMPLING SIEVE jg ^^^^^^ ^f Ulilk ( I7.5 CC. ) 

is found to be more or less below i8 grams according 
to the increased percentage of fat in the cream, run- 
ning even below 17 grams in very rich cream. (3) 
Separator cream is more or less filled with bubbles of 
air, and ripened cream contains gases produced by 
fermentation. These decrease the weight of a given 
volume of cream. 

For the preceding reasons, the result of trying to 
measure by pipette a sample of cream to be used for 
testing its fat content is that less cream will be used 
than should be, and therefore the results will be too 
low. Any system of volumetric measurement pro- 
posed is open to some uncertainty and inaccuracy. 
The use of a pipette in testing cream is justifiable only 
for work that is not expected to be strictly accurate. 



TESTING CREAM BY THE BABCOCK TEST 75 

If one uses a pipette in measuring cream for test- 
ing, somewhat more accurate results are generally ob- 
tained by measuring i8 cc. of cream and also rinsing 
the pipette into the test-bottle with a small amount of 
water. Pipettes are obtainable which have an i8 cc. 
mark as well as a 17.6 cc. 

WEIGHING SAMPLE OF CREAM 
The operation of weighing cream is simple. One 
places the empty test-bottle on one pan of the scales 
and balances it by a slide-weight or some form of 
counterpoise. One then places an 18-gram weight 
on the other pan, after which the pipette is filled with 
cream somewhat above the 17.6 cc. mark, and this is 
run into the bottle, the last portion being run in more 
slowly, until the two scale-pans just counterbalance 
each other. A little practice enables one to weigh 
the exact amount rapidly. In case the amount of 
cream taken in the pipette is not enough, agitate 
the sample, draw a little more into the pipette and 
run this slowly into the bottle until it counter-bal- 
ances the weight. In case too much cream is run 
into the bottle, the surplus can easily be withdrawn 
by the pipette. No cream must be allowed to get on 
the outside of the bottle or on the scale-pan while the 
weighing is done. 

Using less than 18 grams. — In case of very rich 
cream it is preferable to use 9 grams for a sample, in 
which case the reading of the fat-column is multiplied 
by 2; or the 18-gram sample may be divided between 
two cream-bottles, in which case water should be ad- 
ded to each bottle so as to bring the liquid to about 
18 cc. in volume. The results of the test in the two 



76 MODERN METHODS OF TESTING MILK 

bottles are added. It is more convenient after a little 
practice to weigh exactly 9 or i8 grams than to run 
in an approximate amount of cream and weigh that 
accurately. 

In case one uses any amount less than 18 grams for 
a sample, it is necessary to correct as follows the per 
cent, of fat read: Divide 18 by the number of grams 
of cream used and multiply the result by the per cent, 
of fat read in the test. For example, one uses 13.5 
grams of cream and the result reads 15.6 per cent, of 
fat. Divide 18 by 13.5, which gives 1.33, and multiply 
this by 15.6, which equals 20.8 per cent., the true per- 
centage of fat in the sample. 

SPECIAL POINTS ABOUT TESTING CREAM 

When one uses 18 grams of cream in one test-bot- 
tle, the operation is completed as in testing milk. 
When one uses less than 18 grams in one test-bottle, 
enough water is added to make the volume about 18 
cc. Thus, when an 18-gram sample is divided be- 
tween two bottles, or a 9-gram sample in one bottle 
is used, we add 9 cc. of water to the cream, mix them 
thoroughly and then proceed as usual. The water and 
cream should always be well mixed before adding 
acid. 

When it is difficult to get a clear column of fat, it 
may be remedied by the use of a little less acid, the 
exact amount to be found by trial. In general, the 
richer the cream, the less acid is required, 15 cc. often 
being enough. The full amount of acid is used when- 
ever the cream is diluted with water before adding 
acid, as in the case of taking a 9-gram sample, or di- 
viding an 18-gram sample between two cream-bottles. 



TESTING CREAM BY THE BABCOCK TEST 7/ 

Sometimes it is well to let the bottles stand a little 
while after being mixed with the acid, until the mix- 
ture turns dark, before whirling. 

When the liquid just below the fat-column is milky 
and the fat looks cloudy and light, exact reading is 
difficult. In such cases the bottles may be placed in 
water at 130° to 140° F. for 15 or 20 minutes before 
whirling, or, if this fails, the fat may be solidified by 
placing the bottles in cold water after the last whirl- 
ing and then heated to 130° or 140° F. before reading. 

READING THE PER CENT. OF FAT IN CREAM- 
TESTING BOTTLES 

In reading the results of a cream test, more care 
is needed than in testing milk, especially if wide- 
necked bottles are used in which the finest divisions 
represent .5 per cent, or more. For accurate work, 
one should use narrow-necked cream-bottles in which 
the results can be read to .2 per cent. 

In no case, should there be used in the same cream- 
ery at the same time different varieties of cream-bot- 
tles, having necks of widely-varying diameter. It 
has been shown by Webster (Bulletin No. 58, Bureau 
of Animal Industry, Dairy Division, U. S. Dept. of 
Agr.), that the results obtained with cream-bottles 
having necks of varying diameters are wide apart, 
when read in the ordinary manner. This is due to 
the fact that the depth of the meniscus increases with 
the diameter of the neck of the bottle. The wider the 
neck the greater the error, this being in the direction 
of too high results. 



CHAPTER VI 

Methods of Testing Skim-Milk, Whey. Butter, 
Cheese, etc., by the Babcock Test 

Dairy products, such as cheese, condensed milk, and 
milk powders can be tested for fat by the Babcock 
test, and also by-products such as skim-milk, butter- 
milk and whey. In general, the operation is carried 
out as in testing milk, but some special modifications 
are necessary. 

METHOD OF TESTING SKIM-MILK, WHEY, ETC. 

In testing materials containing only .2 or .3 per cent, 
of fat, two difficulties are experienced : ( i ) In the 
ordinary test-bottle, the reading of so small amounts 
of fat can not be easily done with accuracy. (2) Some 
fat is necessarily left in the mixture of acid and milk- 
serum, which may constitute an important factor when 
the total fat content is small. 

Special forms of test-bottles used in testing whey, 
etc. — To enable one to make readings of small amounts 
of fat with increased accuracy, special forms of double- 
necked test-bottles have been devised, which are so 
graduated as to enable readings to be made as low 
as .01 per cent. (Figs. 34 and 35). In using these 
bottles, the milk and acid are delivered into the larger 
neck, the fat being driven up into the small neck by 
the hot water added toward the end of the test. 

78 



TESTING SKIM-MILK, WHEY, CHEESE, ETC. 79 

Enough water is added to bring the fat-cohimn into 
the middle of the small neck. In mixing milk and 
acid and in running in hot water, care must be taken 
to prevent any liquid but fat going into the small neck 
or fine measuring-tube. The stoppers in the bottles 




FIG- 34 FIG. 35 

BOTTLES FOR TESTING SKIM-MILK 

are used to adjust the fat-column for reading. These 
double-necked bottles should be placed in the tester 
in such a way that the filling-tube is toward the center, 
thus avoiding the danger of having any fat caught 
between this tube and the side of the botde when re- 
suming the upright position after whirling. 

Separating fat from mixture in bottle. — Attention 
has previously (p. 64) been called to the difficulty ex- 
perienced in separating all the fat from the mixture 



8o MODERN METHODS OF TESTING MILK 

of acid and milk-serum. Under ordinary conditions 
of working, materials low in fat, like skim-milk, may 
fail to give up to the fat-column .05 or even .1 per 
cent, of fat. Some double the reading of fat when it 
is below .1 per cent, in order to make allowance for 
the unseparated fat. The fat may be separated from 
the rest of the liquid more completely by proceeding 
as follows : Use 20 cc. of sulphuric acid, whirl the bot- 
tles at full speed one or two minutes longer than 
usual and read the fat when at a temperature of 130° 
to 140° F. Steam-turbine testers, which keep the bot- 
tles hot, give best results. Any test of these by-pro- 
ducts showing less than .05 per cent, of fat is open to 
the suspicion of being defective. 

Skim-milk and buttermilk are treated alike. In 
working with whey, it is noticeable that after adding 
acid the mixture turns dark very slowly, due to the 
presence of less sugar and to the absence of casein. 
Less than the usual amount of acid is sufficient for 
whey, 8 or 10 cc. frequently being sufficient. 



METHOD OF TESTING CHEESE 

In applying the Babcock test to cheese, it is neces- 
sary to prepare the sample in a special way and to 
weigh the amount used. A 9-gram sample is a con- 
venient amount to use, in which case the reading of 
fat is multiplied by 2 ; or an 18-gram sample may be 
divided between two cream-bottles, the final readings 
being added. Cream-testing bottles graduated to .2 
per cent, divisions should be used. 



TESTING SKIM-MILK, WHEY, CHEESE, ETC. 8l 

Sampling cheese for fat-test. — Since different por- 
tions of the same cheese vary in composition, special 
means must be used to get a representative sample. 
The sample for testing is prepared as follows : When 
a cheese can be cut, a narrow, wedge-shaped seg- 
ment is taken, reaching from the outer edge to the 
center. This is cut into strips and passed through a 
meat-grinding machine two or three times. This mass 
is carefully mixed, and from this a 9-gram sample is 
weighed into a cream-testing bottle, or a 4.5-gram 
sample into an ordinary milk-testing bottle. 

When cheese can not be cut, samples are obtained 
by a cheese-trier. If possible, three plugs should be 
drawn, one at the center, one about an inch from the 
outer edge, and one at a point half way between the 
other two. If only one plug can be drawn, this should 
be taken at a point about half way between the mar- 
gin and center. The plugs should be taken perpen- 
dicular to the end surface of the cheese and should 
reach either entirely through the cheese or just half 
way. The plugs should be made fine by grinding or 
cutting and carefully mixed before' weighing samples. 
In preparing samples, they should not be exposed to 
the air longer than necessary, since loss of moisture 
should be prevented as much as possible before weigh- 
ing. 

Testing sample of cheese. — The sample is weighed 
into the bottle. Then one adds about 15 cc. of hot 
water in the test-bottle and agitates until the water 
disintegrates the cheese ; this may be hastened by add- 
ing a few cubic centimeters of acid, and keeping the 
bottle in slightly warm water. When no more lumps 



82 MODERN METHODS OF TESTING MILK 

are seen in the liquid, 17.5 cc. of sulphuric acid is 
added. The test is then completed in the usual way. 
To obtain the per cent, of fat in the cheese, if less 
than 18 grams is used, multiply the reading of fat 
by 18 and divide by the number of grams of cheese 
used in the test. 

METHOD OF TESTING BUTTER 

The Babcock test has not been adapted to deter- 
mine accurately the amount of fat in butter. A mass 
of butter is so variable in its composition, owing to 
the uneven distribution of water, that it is difficult to 
obtain a representative sample when only a small 
amount is used. Since butter contains over 80 per 
cent, of fat, a sample of less than 9 grams must be 
used in a test-bottle made to measure less than 40 
per cent, of fat. Approximate results can be obtained 
by observing certain precautions. 

Preparing sample of butter. — With a butter-trier 
draw several samples, aggregating 4 to 8 ounces. 
Place these samples in a fruit- jar or composite-sam- 
ple bottle, melt completely by placing in fairly hot 
water with the jar closed; then remove from hot wa- 
ter and shake vigorously for one or two minutes, after 
which moderate agitation is continued until the but- 
ter solidifies. The cooling may be hastened by hold- 
ing the jar under a stream of cold water, continuing 
to shake the bottle vigorously until the butter hardens. 

Testing sample of butter. — On a cream-scale place 
a cream-bottle (Fig. 29, p. 70), in which is placed a 
long-stemmed cylindrical funnel (Fig. 36). After 
balancing the bottle and funnel, one takes on the 



TESTING SKIM-MILK, WHEY, CHEESE, ETC. 



83 



point of a knife from different parts of 
the sample of butter, prepared as above 
described, small pieces of butter and 
places them in the funnel until the sam- 
ple weighs 5 grams. The bottle and 
funnel are heated until the butter runs 
into the test-bottle. The tube is then 
rinsed with 10 cc. of hot water and the 
same amount of acid is added. The test 
is completed in the usual manner. The 
final reading of fat should be at about 
120° F., and the results corrected in the 
usual manner. Instead of 5 grams one 
can weigh 9 grams and divide it approx- 
imately between two cream-bottles, add- 
ing the final results, and multiplying the 
sum by 2. 



METHODS OF TESTING 
CONDENSED MILK 



FIG. 36 

GLASS FUNNEL 

FOR USE IN 
TESTING BUTTER 



For condensed milk containing no added sugan — 

The following methods can be used: 

(i) Weigh 9 grams into a milk-testing bottle, add 
about 10 cc. of water and then the usual amount of 
acid. Complete the test as for milk. Multiply fat- 
reading by 2. 

(2) Weigh 40 grams of the well-mixed sample into 
a 100 cc. glass cylinder, such as is used in the alkaline- 
tablet test (Fig. 38, p. 96). Add water to the 100 cc. 
mark and shake until well mixed. Then, with a 17.6 
cc. pipette, take for testing a sample of this solution, 
representing 7 grams of the undiluted sample, and 



84 MODERN METHODS OF TESTING MILK 

complete the test as usual. Multiply the fat-reading 
by 1 8 and divide by 7 to find the correct per cent, of 
fat in the sample. 

(3) Approximate results may be obtained by di- 
luting a measured amount of condensed milk with an 
equal volume of water, agitating the mixture until 
uniform. Then take sample for testing with a 17.6 
cc. pipette and proceed as usual. The per cent, of fat 
read is multiplied by 2. 

For condensed milk containing added sugar. — 
Many brands of condensed milk contain added cane 
sugar, which in testing is so blackened by the acid as 
to make the results unreliable. This trouble can be over- 
come by special treatment devised by Farrington. 
Make a solution of 40 grams of condensed milk in 
100 cc. of water, as directed above in (2). With a 
17.6 CC. pipette, measure the same amo'imt as for a 
milk test into a milk-testing bottle. Add about 3 cc. 
of the sulphuric acid used in the test and mix the 
acid and milk by shaking vigorously. The acid is added 
to coagulate the curd and enclose the fat, allowing 
the sugar to separate in the surrounding liquid. The 
curd is compacted into a lump by whirling the test- 
bottles in a steam-turbine tester at high speed and at 
a temperature of 200° F. After this whirling, the 
bottles are taken from the tester and the liquid portion, 
containing much of the sugar, is carefully poured 
from the neck without breaking the lump of curd. 
Then an addition of 10 cc. of water is made to the 
test-bottles, the curd is shaken up to wash out more 
sugar, and again 3 cc. of sulphuric acid added. The 
bottles are again whirled and the liquid portion de- 



TESTING SKIM-MILK, WHEY, CHEESE, ETC. 85 

canted. Then the test is completed by adding lo cc. 
of water, 17.5 cc. of sulphuric acid, and proceeding as 
usual. Correct the fat-reading by multiplying by 18 
and dividing by 7. 

METHOD OF TESTING FOR FAT IN INFANT 
FOODS 

Some infant foods contain so much sugar that, like 
sweetened condensed milk, it is impossible to use the 
Babcock test unmodified. Cochran recommends a 
method for the determination of fat in such cases, 
which he has found very useful (Journal of the Amer- 
ican Chemical Society, Vol. 2y, p. 908). A double- 
tubed test-bottle is used, the larger tube reaching only 
a short distance into the bowl of the bottle. 

To determine fat in sweetened condensed milk, make 
a solution of the condensed milk in the manner given 
above under (2). Of this solution put 17.5 cc. in the 
test-bottle, add 9 cc. of 80 per cent, acetic acid and 
9 cc. of strong sulphuric acid. Mix the acids and milk 
and set the bottle in hot water until the mixture in 
the bottle turns a coffee-brown color. Then remove 
the bottle, cool, add 15 cc. of ether and mix thoroughly 
with the liquid. The flask is again placed in hot wa- 
ter and the ether allowed to evaporate. A layer of 
fat will appear floating on the surface of the liquid. 
By pouring hot water into the side tube, the liquid 
fat is raised into the graduated tube, where its amount 
can be read. The reading is corrected by multiplying 
by 18 and dividing by 7. 

In the case of powdered infant foods, like malted 
milk, weigh 6 grams of the powder into the bottle, 



86 MODERN METHODS OF TESTING MILK 

add 17.5 cc. of water, dissolve the powder as com- 
pletely as possible, and proceed as above. Multiply 
the reading by 3. 

METHOD OF TESTING DRIED MILK OR MILK 
POWDER 

Successful means of drying milk have recently been 
devised, and products are appearing on the market in 
the form of dried skim-milk and dried milk. These 
materials are in the form of fine flaky or powdery 
substances. Owing to the great advantages of hand- 
ling milk in such forms, these products are destined 
to find extensive use, and the desirability of testing 
them is obvious. 

The Babcock test, when applied to these materials, 
gives results much^ below the truth. The writer has 
obtained quite satisfactory results by a combination of 
the Gottlieb and Babcock methods of determining fat. 
The process used is as follows : Dissolve 10 grams of 
milk powder in 100 cc. of water. Take 10 cc. of this 
solution in a 100 cc. glass cylinder (Fig. 38, p. 96). 
Add I cc. of strong ammonia and shake until thor- 
oughly mixed with the solution. Then add the fol- 
lowing reagents, one after the other, shaking vigorously 
after each addition before adding the next material: 
10 cc. of 92 per cent, alcohol, 25 cc. of washed ether, 
and 25 cc. of gasoline or, better, petroleum ether 
(boiling point below 80° C). The cylinder is closed 
with a tightly-fitting, moistened cork stopper. The 
contents of the cylinder, after thorough shaking, are 
poured into a 200 cc. beaker, the cylinder being rinsed 
with a little gasoline, and this being added to the 



TESTING SKIM-MILK, WHEY, CHEESE, ETC. 8/ 

beaker. The beaker, is then placed on a steam-bath 
or in boihng- water and kept there until the ether, alco- 
hol and gasoline are completely evaporated. The re- 
maining liquid is then poured into a milk-testing bot- 
tle, the beaker is rinsed with a little ether, which is 
also added to the test-bottle. The test-bottle is then 
placed in boiling water a few minutes to evaporate 
the ether. After cooling the contents of the test-bot- 
tle to about 70° F., one adds 17.5 cc. of sulphuric acid 
and completes the operation as in the case of milk by 
the Babcock test. The reading is multiplied by 18. 
In some cases, as in dried skim-milk, it will be desira- 
ble to make the original solution more concentrated 
by having 20 or more grams in 100 cc. of solution. 
The following precautions must be observed in using 
this method: 

(i) The milk-powder solution must be made uni- 
form before sampling. 

(2) The shaking of the mixture must be vigorous 
and thorough after the addition of each of the reagents 
used. 

(3) The evaporation of the reagents added must be 
complete; otherwise, the final results are apt to be 
too high. 

(4) The evaporation must not be carried so far as 
to cause any appearance of solid particles in the liquid. 
When this happens, the fat-column contains dark ma- 
terial, which makes the results uncertain. 

This method is applicable to skim-milk, whey and 
buttermilk, which do not usually give high enough re- 
sults by the Babcock method. 



CHAPTER VII 



Methods of Testing the Acidity of Milk and Milk 
Products 

It is often necessary to know how much acid is 
present in milk, cream, whey, etc. The amount of 
acid in milk may be a suggestive indication of the 
age of milk and of its care. In butter-making, the 
uniformity of the product depends largely upon the 
ripening of cream, which can be well controlled only 
by knowing its acidity. In cheese-making, it is at 
times important to know whether milk contains too 
much acid and it is also quite essential to have some 
knowledge of the amount of acid present in the milk 
and whey at different stages of the operation. 

THE CAUSES OF ACIDITY IN MILK AND ITS 
PRODUCTS 

We may distinguish two kinds of acidity in milk 
and its products: (i) Apparent acidity, and (2) acid- 
ity due to lactic acid. The apparent acidity is due to 
the presence in normal milk of casein and acid phos- 
phates, which have the power, like free acids, of neu- 
tralizing alkalis. This apparent acidity in fresh milk 
is about .07 or .08 per cent, on the average. It varies 
with different conditions, increasing, for instance, with 
advance of lactation. 

Acidity due to lactic acid is formed in milk after it 
is drawn, and is caused by the action of certain forms 

88 



TESTING ACIDITY OF MILK AND MILK PRODUCTS 89 

of bacteria upon milk-sugar. In general, when milk 
contains over .10 per cent, of acid, it may safely be 
assumed that it contains some lactic acid. The amount 
of lactic acid present in milk may be approximately 
found by subtracting .10 from the total amount of 
acid apparently present. However, in speaking of the 
acidity of milk, we usually mean the total acidity, and 
not that due to lactic acid alone. One can not com- 
monly detect a sour taste in milk that has a total acidity 
under .3 per cent. 

GENERAL PRINCIPLES OF TESTING ACIDITY 

The method of determining the amount of acid in 
milk and its products is based upon the well-known 
chemical action taking place between acids and alka- 
lis. Whenever we bring together in solution an acid 
and an alkali, they combine with each other and form 
a third compound, the acid and alkali disappearing as 
such. The acid and alkali are said to neutralise each 
other and the process is called neutralization. For 
example, if we add together some hydrochloric (muri- 
atic) acid and sodium hydroxide (caustic soda) in 
right proportions, we shall have neither hydrochloric 
acid nor caustic soda, but a new compound, sodium 
chloride (common salt), which has been formed by 
the action of the acid and alkali upon each other. The 
hydrochloric acid used in the experiment tastes sour 
and biting, while the caustic soda solution has a pecu- 
liar odor, feels soapy on the skin, and, if strong enough, 
destroys the skin. After these two compounds are 
brought together in proper proportions, there is no 



90 MODERN METHODS OF TESTING MILK 

longer observed any sour taste of acid or soap}^ feel- 
ing or odor of alkali, because the acid and alkali have 
neutralized each other and have combined to form 
simply common salt, the presence of which is noticed 
by its taste. The solution is said to be neither alkaline 
nor acid, but neutral. 

USE OF INDICATORS IN TESTING ACIDITY 

In working with acids and alkalis, it is necessary 
to have some simple means of knowing when a solu- 
tion is acid, alkaline or neutral (neither acid nor alka- 
line). This can be found by using some substance, 
called an indicator, which is so acted on by alkalis 
and acids as to undergo changes of color, being 
changed one color by alkalis and a different color 
by acids. One substance which finds wide use as an 
indicator is a chemical compound called phcnolphthal- 
ein, a solution of which is turned pink by alkalis and 
colorless by acids. For use in testing acidit}^, one dis- 
solves ID grams of the dry powder in 300 cc. of 90 
per cent, alcohol. It is necessary to use only 5 or 10 
drops of this solution as indicator. 

GENERAL APPLICATION OF PRINCIPLES OF 
NEUTRALIZATION 

What use can be made of the foregoing facts in 
finding the per cent, of acid in a solution? For sim- 
plicity, we will use the following illustrative experi- 
ment: In a glass or teacup we put 100 cc. of a solu- 
tion containing .25 per cent, of lactic acid and add 5 
or 10 drops of indicator solution. Into this mixture 



TESTING ACIDITY OF MILK AND MILK PRODUCTS 9I 

we run from a graduated cylinder or burette some 
standard solution of caustic soda, prepared by dis- 
solving 4 parts by weight of pure caustic soda in i,ooo 
parts of distilled water. This solution of caustic soda 
we add, a little at a time, to the solution of lactic 
acid, stirring or otherwise agitating the mixture thor- 
oughly after each addition. The pink color that ap- 
pears when the caustic soda solution is added disap- 
pears on stirring. After the alkali has been added 
several times, the color disappears less rapidly each 
time. The gradual addition of the alkali is continued 
until finally the pink color does not disappear readily 
on continued agitation but remains for some moments. 
The neutralization of the acid by the alkali is complete, 
and the addition of alkali stops at this point. The ap- 
pearance of the pink color throughout the body of the 
liquid means that enough alkali has been added to 
combine with the lactic acid, and a little more, one 
drop of the alkali solution being enough to produce 
the pink color with the indicator after the acid is neu- 
tralized. The liquid in the cup contained at the start 
only a solution of lactic acid. As soon as we added 
alkali, it combined with the lactic acid, forming the 
neutral compound, sodium lactate. We then had a 
mixture of lactic acid and sodium lactate. As we con- 
tinued to add alkali, the amount of sodium lactate in- 
creased, while the amount of lactic acid decreased. 
Finally, a point is reached when the solution in the 
cup contains no free lactic acid, but only sodium lac- 
tate, and the addition of one more drop of alkali turns 
the indicator pink, producing a more lasting coloration 
throughout the solution and showing that the acid 



92 MODERN METHODS OF TESTING MILK 

has been completely neutralized, that is, changed into 
sodium lactate. 

Having completed the neutralization of the acid, 
we examine the burette or the graduated cyhnder con- 
taining the alkali to find exactly how much alkali so- 
lution has been used in neutralizing the acid. The 
lactic acid has required, say, 28 cc. of soda solution. 
Each cubic centimeter of alkali neutralized by acid 
corresponds to .009 gram of acid, and 28 cc. would 
therefore correspond to .25 gram of lactic acid. This 
amount of lactic acid in 100 cc. is .25 per cent. The 
process of making a chemical determination by means 
of a standard solution is known as titration. 

NEUTRALIZATION METHOD APPLIED TO TEST- 
ING ACIDITY OF MILK AND MILK PRODUCTS 

In practical dairy work, one is freed from the ne- 
cessity of preparing standard solutions, except in a 
simple way, and the calculations needed to figure the 
results are direct and easy. The caustic soda solution 
is prepared in such strength that a certain amount of 
it equals .1 per cent, of lactic acid, when a certain 
amount of milk or other substance is used. All tests 
for the acidity of milk and its products are based upon 
the general principles previously described and differ 
from one another simply in some of the details of 
carrying out the process. There are now available sev- 
eral forms of so-called acid tests, among which we 
shall describe the following: "Mann's acid test," 'Har- 
rington's alkaline-tablet test," and the Purdue alkali 
test." 



TESTING ACIDITY OF MILK AND MILK PRODUCTS 93 



DESCRIPTION OF MANN'S ACID TEST 



Apparatus and materials. — The apparatus and ma- 
terials used in this test are : ( i ) A 50 cc. glass burette, 
with stopcock, (2) a 50 cc. pipette for measuring sam- 
ples, (3) a glass beaker and stirring-rod, (4) 
an alcoholic solution of phenolphthalein, 
and (5) a standardized alkali solution la- 
beled "neutralizer," each cubic centimeter 
of which contains enough sodium hydrox- 
ide (.004 gram) to neutralize .009 gram 
of lactic acid. The outfit is shown in Fipf. 

Operating the test. — (i) Measuring 
sample. — Into a clean beaker or white por- 
celain cup, one measures 
with the pipette exactly 50 
cc. of the material (milk, 
cream, etc.) to be tested. 
The pipette is then rinsed 
by filling with water, pre- 
ferably distilled, and this 
rinsing water is added to the sample. 

(2) Adding alkali. — The indicator (5 or 10 drops) 
is then added to the sample. The burette is then filled 
to the zero mark with the neutralizer, and some -of it 
is run into the sample in the beaker or cup. A pink 
color appears, but disappears on stirring. The addi- 
tion of alkali in portions is continued with care, the 
sample being stirred after each addition. It will be 
noticed sooner or later, according to the amount of 
acid present, that, after each addition of alkali, the 




FIG. 2>7 — MANN S ACID TEST 



94 MODERN METHODS OF TESTING MILK 

pink color disappears more slowly, showing that the 
acid is becoming Biore nearly neutralized. When the 
color disappears quite slowly, the neutralizer should 
be added a drop at a time. Finally a point is reached 
when, after the addition of one drop of alkali, the 
pink color does not disappear even after stirring lo 
or 15 seconds. This indicates that the acid is com- 
pletely neutralized. Add no more alkali. The pink 
color will slowly disappear after standing some time, 
even when the solution is alkaline. Some experience 
enables one easily to know when the pink color is suf- 
ficiently permanent. 

(3) Calculating results. — Having completed the ad- 
dition of alkali, the burette is examined to see how 
many cubic centimeters of neutralizer have been used. 
The percentage of acid for 50 cc. or any amount of 
sample taken is calculated from the following for- 
mula : 



Per cent, of acid=g2.^£-4^MiAJ59 xioo. 

No. cc. of sample taken 



When one uses 50 cc. of the sample, this formula 
becomes 

Per cent, of acid = No. cc. of alkali X .018. 

From this last formula one can prepare a table which 
gives the results and saves making calculations at 
every test: 



TESTING ACIDITY OF MILK AND MILK PRODUCTS 95 
c c OF ALKALI SOLUTION. Pfr ceut. of add 

(NEUTRALIZER) USED i^ Samplc tCStcd 

J 0x8 

2 . . 036 

3 ' 054 

4 '. -072 

5 , . .09 

10 ^8 

15 ^7 

20 36 

30 .54 

40, etc. 72, etc. 

By using the first formula above, similar tables can 
be prepared when the amount of sample taken is any 
amount other than 50 cc. 

Using Babcock Pipette with Mann's Test.— If a 
17.6 cc. pipette is used in measuring the liquid to be 
tested, the percentage of acid may be found by divid- 
ing by 2, the number of cubic centimeters of Mann's 
alkali used, the result being expressed a*s tenths per 
cent. Thus, if the liquid tested neutralizes 13 cc. of 
alkali, the acidity is 13 divided by 2, which, expressed 
as tenths, is .65 per cent. By diluting Mann's "neutral- 
izer" with an equal volume of water, the number of 
cubic centimeters gives directly the percentage of acid- 
ity, expressed as tenths. 

FARRINGTON'S ALKALINE-TABLET TEST 

Apparatus and materials. — In this method the 
same chemical principles are employed as in Mann's 
test, but the alkali, in the form of a carbonate, and in- 
dicator are mixed together in the form of solid tab- 
lets. Each tablet contains enough alkali to neutralize 



96 



MODERN METHODS OF TESTING MILK 




.034 gram of lactic acid. The apparatus (Fig. 38) 
consists of a 17.6 cc. pipette, a white porcelain cup, and 
a 100 cc. graduated glass cylinder provided with a 
rubber stopper. 

Preparing the alkali solution. — In using the alka- 
line tablets, one first puts 5 tablets into the graduated 

100 cc. cylinder, and fills 
this to the 97 cc. mark with 
clean, soft water, prefera- 
bly distilled. The cylinder 
is then tightly corked and 
laid on its side until the 
tablets dissolve, which re- 
quires several hours. The 
cylinder must be kept 
tightl}^ corked so that 
none of the solution can be lost while the tablets are 
dissolving. A slight flocculent residue will not dis- 
solve, consisting of some inert matter used in the mak- 
ing of the tablets. 

Precautions in using alkali solution. — The solu- 
tion should always be shaken well before using. It 
should always be kept tightly stoppered when not in 
use. The solution, if kept perfectly stoppered, will 
not greatly change in a week. Solutions older than 
this may change their strength and should not be used. 
It is a wise precaution to throw away solutions previ- 
ously used for some days and to prepare a fresh solu- 
tion. The solid tablets do not change if kept dry. 

Operation of alkaline-tablet test. — The material 
(milk, cream, etc.) to be tested is thoroughly mixed, 



FIG. 38 — FARRINGTOn's 
ALKALINE-TABLET TEST 



TESTING ACIDITY OF MILK AND MILK PRODUCTS 97 



and 17.6 cc. is then measured into a clean porcelain 
cup with a pipette. The pipette is rinsed by filling with 
water, which is added to the sample in the cup. The 
tablet solution prepared in the manner described is 
poured slowly into the cup in small portions at a time, 
and the mixture is agitated by rotating the cup after 
each addition of alkali. When the pink color does not 
disappear readily on agitating (p. 94), the number of 
cubic centimeters of alkali used is read from the grad- 
uated cylinder. Each cubic centimeter of alkaline-tab- 
let solution used equals .01 per cent, of lactic acid in 
the sample tested. For example, the use of 25 cc. of 
alkali solution equals .25 per cent, of acid; 40 cc. 
equals .40 per cent., etc. 



SPILLMAN'S MODIFICATION OF 
ALKALINE-TABLET TEST 



The apparatus consists of an ordi- 
nary teacup, a regular 17.6 cc. pipette, 
a quart Mason fruit- jar, and "Spill- 
man's acid-test cylinder" (Fig. 39). 
The alkali solution is prepared by dis- 
solving alkaline tablets in water at 
the rate of 5 tablets for one cylinder 
of water filled to the mark 8, the so- 
lution being made and kept in the 
fruit- jar. Observe the precautions 
given above in using tablet solutions. 
In making the test, put 17.6 cc. of 
the material to be tested in a teacup, 
pour into the cup the alkali solution in the manner de- 
scribed above, until the pink color remains. Then 



t- 



FIG. 39 

spillman's acid- 
test CYLINDER 



98 MODERN METHODS OF TESTING MILK 

pour the contents of the teacup into the SpiUman cyl- 
inder and read the scale at the surface of the liquid 
in the cylinder. The results indicate the acidity in 
tenths of one per cent. The cylinder reads as high as 
8 tenths. 



TABLET TEST MODIFIED FOR RAPID ESTIMA- 
TION OF ACIDITY 

It is often desirable to ascertain quickly whether 
milk or cream contains more or less than .2 or .3 per 
cent, of acid. Farrington and WoU have devised the 
following method: An alkali solution is prepared by 
dissolving in an 8-ounce bottle 2 tablets for each 
ounce of water used. A No. 10 brass cartridge shell, 
on which a wire handle is soldered, is used for meas- 
uring the sample to be tested and also the alkali. A 
cartridgeful of milk or cream, is placed in a teacup 
and then a cartridgeful of the alkali solution is added. 
The contents of the cup are mixed by a rotary motion. 
If the sample tested remains white, it contains over 
.2 per cent, of acidity; if a pink color remains, the 
acidity is less than .2 per cent. The intensity of the 
pink color indicates the relative amount of acid pres- 
ent, since the color will be more intense in proportion 
as there is less acid. Any other measure may be used 
in place of the brass cartridge-shell, but in every case 
care must be taken to use equal amounts of milk or 
cream and of alkali solution. 



TESTING ACIDITY OF MILK AND MILK PRODUCTS 99 

THE PURDUE ALKALI TEST 

This test was devised by H. E, Van Norman (Bul- 
letin No. 104, Purdue Univ. Agr. Exp. Sta., 1905.) 
The following- apparatus (Fig. 40) is used: (i) An 




A 

I7.6CC 



<=1 

C.C. 

62° F. 
100—0 
90—10 

80 20 

70—30 
60— 4fl 

50 50 

40 — 60 
30—70 

20— eo 

10—90 




DILUTE ALKAU 
SOLUTION 

icc=.or/o WTH^ 

17.6 CC PIPETTE 

i^OF CREAM ETC. J 




CAUSTIC S00« 
SOLUTION 
_37CC.^ 



FIG. 40 — PURDUE ALKALI TEST 

ordinary 17.6 cc. pipette, (2) a 100 cc. cylinder, such 
as is used in the alkaline-tablet test, (3) a 2-quart bot- 
tle graduated at 1850 cc, (4) sealed bottles, each con- 
taining 37 cc. of normal solution of sodium hydroxide 
(caustic soda), (5) a bottle of phenolphthalein indi- 



LOf€. 



100 MODERN METHODS OF TESTING MILK 

cator and (6) an ordinary white teacup. The alkaU 
solution must be of guaranteed accuracy and should 
be obtained only from a reliable chemical or dairy- 
supply house. 

The test is conducted as follows : Into the 1850 cc. 
bottle one empties the small bottle, containing 37 cc. 
of normal alkali solution, rinsing the small bottle with 
water once or twice and adding the rinsings to the 
large bottle, which is then filled to the mark with wa- 
ter, Use only clean, soft or, preferably, distilled wa- 
ter. This large bottle is kept tightly stoppered. Meas- 
ure into a white teacup 17.6 cc. of the material to be 
tested, rinse the pipette with clean water, adding the 
rinse water to the sample in the cup, and then add 
5 or 10 drops of indicator. From the graduated cyl- 
inder, filled to the 100 cc. mark with the dilute alkali 
solution, one pours the solution in portions into the 
sample to be tested, agitating after each addition of 
alkali, and continuing the addition of alkali solution 
until the pink color does not disappear on agitation. 
Then, from the cylinder read the number of cubic cen- 
timeters of alkali used. Each cubic centimeter corre- 
sponds to .01 per cent of acid. 

COMPARISON OF DIFFERENT FORMS OF 
ACID TESTS 

Mann's acid test has the advantage of furnishing 
the alkaline solution ready for use at any time. It 
has this serious disadvantage, that the alkaline solu- 
tion is in constant danger of becoming weakened by 
absorption of carbon dioxide when exposed to the air. 
A weakened alkali solution gives higher results of 



TESTING ACIDITY OF MILK AND MILK PRODUCTS lOI 

acidity than the truth. . It has also the disadvantage of 
requiring a calculation to obtain the results in the 
form of per cent., and any other form of statement 
ought not to be used. 

The alkaline-tablet test has the advantage of giving 
the results directly in percentages. The tablets do not 
change is kept dry, and the use of a fresh solution 
avoids all uncertainity of strength. The cost of trans- 
portation is insignificant compared with that of the 
neutralizer. The tablets are not always absolutely 
uniform in strength of alkali, but the variations are 
not sufficient to make serious differences in results. 

In the Purdue modification, the small bottles of al- 
kali do not lose strength so long as they are kept 
properly stoppered, and therefore any number can be 
ordered at a time. Being more concentrated than 
Mann's neutralizer, the cost of transportation is less. 
The solution is more quickly and conveniently prepared 
than the tablet solution. The strength of the small 
bottles of alkali is said to be more strictly uniform than 
in the case of tablets. By high dilution of the alkali 
solution when used, the chance of error is reduced. 

TESTING THE ACIDITY OF WHEY 

Whey may be tested by any of the methods de- 
scribed. Owing to the comparatively low acidity of 
whey in the operation of cheese-making, it is desirable 
either to have the alkali dilute ( i cc. of alkali equal to 
.01 per cent, acid), or else to take twice as much whey 
for testing as in the case of cream, the final results 
being corrected by dividing by 2. The whey should 
be free from particles of curd, since curd has the 



I02 MODERN METHODS OF TESTING MILK 

power of neutralizing alkali to some extent. The per- 
centage of acid in milk can be used as a guide in 
ripening the milk before adding rennet, in the rate of 
heating (cooking) the curd, in the regulation of the 
piling of the curd, in the time of milling, etc. 

TESTING THE ACIDITY OF CHEESE 

From a sample of cheese, prepared in the manner 
described on page 8i, weigh nine grams and to this 
add water at a temperature of ioo° to iio° F. until 
the volume equals 90 to 100 cc. Agitate vigorously 
and filter. To the filtrate add alkali solution, each 
cubic centimeter of which equals .01 per cent, of lac- 
tic acid, carrying out the test as with milk, cream, etc. 
The number of cubic centimeters of alkali used, mul- 
tiplied by 2, equals the per cent, of acid in the cheese. 
Much higher results are obtained if one treats the 
cheese instead of its water extract with alkali, because 
the nitrogen compounds of the cheese neutralize alkali. 

RELATION OF FAT IN CREAM TO ACIDITY OF 
CREAM-RIPENING 

Cream rich in fat ripens, that is, becomes acid, more 
slowly than cream poor in fat. This is so, because the 
larger the percentage of fat in cream the smaller is 
the percentage of sugar, and the sugar is the source of 
lactic acid. The favorable influence of ripening upon 
the process of churning is believed to be due to the 
action of the acid upon the calcium casein of the cream, 
converting it into calcium lactate and so lessening its 
tenacious hold upon the fat-globules in emulsion. The 
fat itself of the cream is not changed. The amount 



TESTING ACIDITY OF MILK AND MILK PRODUCTS IO3 

of acid to be formed in cream-ripening is, therefore, to 
be governed more by the amount of calcium casein in 
the cream than by any other constituent. The less fat 
there is in normal cream, the more casein there will be, 
and the greater the per cent, of acidity needed. The 
more fat there is in cream, the less calcium casein there 
will be, and the less the amount of acid needed. These 
statements conform to practical experience. Thus, 
it is found that in cream containing 25 per cent, of 
fat, it is necessary to produce nearly .7 per cent, of 
acid in order to get the results sought by ripening, 
while, in cream containing 35 per cent, of fat, less 
than .6 per cent, of acid is sufficient. 

To ascertain how much acid should be formed in 
cream before churning, the following rule is suggested 
by Van Norman (Bulletin 104, Purdue Univ. Agr. 
Exp. Sta.) : From 100 substract the per cent, of fat 
in the cream tested and multiply the result by .9, or, 
expressed as a formula, (100 — per cent, of fat in 
cream) X.9. For example: 

Cream with 20 per cent, fat requires .72 per cent, of 
acidity. 

Cream with 25 per cent, fat requires .67 per cent, of 
acidity. 

Cream with 30 per cent, fat requires .63 per cent, of 
acidity. 

Cream with 35 per cent, fat requires .58 per cent, of 
acidity. 

The use of .9 as a factor for multiplying may not 
suit all conditions and some other factor, .8 for exam- 
ple, may be used. Each operator may experiment and 



I04 MODERN METHODS OF TESTING MILK 

easily find what per cent, of acidity is best adapted to 
the production of the butter suiting his market, and 
then a table like the above can be made, using .9 or 
some other factor. 

OUTLINE STATEMENT OF SOME SPECIAL 
PRECAUTIONS IN TESTING ACIDITY 

1. The material to be tested for acidity must be 
thoroughly mixed before sampling for a test. 

2. The water used in preparing the alkali solution 
and in rinsing the pipette should be neither acid nor 
alkaline and should be soft and clean. Use distilled 
water if possible. 

3. The alkaline tablets should be kept dry in well- 
stoppered bottles. 

4. The alkali solution, in whatever form used, must 
be kept from contact with the air as much as possible 
to prevent changing strength either through evapora- 
tion or absorption of carbon dioxide. 

5. When alkaline tablets are used, prepare a fresh 
solution in order to be sure of its strength, if there is 
any reason for uncertainty. 

6. The tests should be made in a good light so that 
one can easily see the appearance of the longer-lasting 
pink color at the end of the reaction. 

7. The appearance of the pink color at the end of 
the test can usually be more sharply seen by diluting 
the material examined with three or four times its vol- 
ume of distilled water. 



CHAPTER VIII 

Method of Testing the Bacterial Condition of 
Milk 

A thorough bacteriological examination of milk re- 
quires somewhat extended special training, but there 
are methods for ascertaining the general bacterial con- 
dition of milk which are available in the hands of any 
careful worker, and which afford most valuable sug- 
gestions in regard to the cleanliness of milk. The 
methods of studying the bacterial condition of milk 
which we shall notice are (i) determining the acidity, 
(2) the fermentation method known in its most avail- 
able form as the "Wisconsin Curd-Test," and (3) test- 
ing for dirt in suspension. 

THE RELATION OF ACIDITY TO THE BACTE- 
RIAL CONDITION OF MILK 

The details of the method of determining acidity in 
milk have been given in Chapter VII. We need say 
here only a few words in regard to the interpretation 
of the results as they relate to the cleanly character 
of milk and its fitness for use. The amount of acid in 
milk is generally an indication of the care given to the 
milk after being drawn from the cow ; to some extent, 
it indicates the age of the milk, especially if the tem- 
perature at which it has been kept, is known ; and, if 
the age of the milk is known, the acidity indicates, to 
some extent, the temperature at which the milk has 

105 



I06 MODERN METHODS OF TESTING MILK 

been kept. The cleanliness of the milk-pails and other 
vessels and utensils with which the milk conies in con- 
tact is another important factor in influencing acidity. 
The average acidity of English market milk, sup- 
posed to be 12 to i8 hours old, is .18 per cent, and of 
German milk, .13 to .18 per cent. Alarket milk should 
not, in any case, contain over .2 per cent of total acid- 
ity when it reaches the consumer, and should generally 
be under .15 per cent. This (.2 per cent.) is also the 
highest limit allowable for milk that is to be used for 
cheese-making. The test for acidity can thus be made 
a very useful indication of the bacterial condition of 
milk so far as it relates to the acidity, and to the 
abundance of those forms that produce lactic acid. 

THE FERMENTATION OR WISCONSIN 
CURD-TEST 

Milk frequently contains objectionable forms of 
organisms or ferments that are not made perceptible 
by ordinary methods of observation. The condition 
arises particularly in milk used for cheese-making and 
may result in serious injury to the quality of the cheese. 
The Wisconsin Experiment Station (Wis. Exp. Sta. 
1 2th and 15th Annual Reports, 1895 and 1898) has 
applied certain principles to the development of a 
test that enables one to identify milk containing cer- 
tain forms of undesirable ferments likely to do serious 
injury. This method is based, in general, upon the 
plan of making conditions favorable for the rapid de- 
velopment of the ferments present in milk. 

Apparatus. — The apparatus consists of the follow- 
ing parts: (i) Pint glass jars or tin cans with covers; 



TESTING THE BACTERIAL CONDITION OF MILK IO7 

(2) a well insulated tank to hold the jars, (3) rennet 
extract, (4) a thermometer, (5) a case-knife or simi- 
lar instrument for cutting curd, and (6) a small pipette 
for measuring rennet-extract. 

Operation of test. — The test is conducted as fol- 
lows : The jars, including covers, just previous to 
use, are sterilized with live steam, scalding water or 
dry heat (212° F.). Each jar or can is filled about 
two-thirds full with the milk to be tested and the ster- 
ilized cover put on at once. The jars are then placed 
in the tank which is filled with water at 100° to 102° 
F. up to the upper surface of the milk in the jars. The 
temperature of the water should be kept at 100° to 
102° F. during the whole operation. To hasten the 
warming of the milk, the jars are taken out and shaken 
occasionally. The temperature of the milk is observed 
with a sterile thermometer, and when the milk has 
reached 98° F., one adds 10 drops of rennet-extract 
to each jar and mixes thoroughly by giving the con- 
tents of the jar a rotary motion. When the milk has 
coagulated, it is allowed to stand until it is firm, usu- 
ally about 20 minutes. To enable the whey to sepa- 
rate more readily, the curd is then cut fine with a 
thin knife, which must be carefully rinsed with hot 
water after finishing each jar and before using it in 
another, in order to avoid carrying contamination from 
one milk to another and spoiling the test. The curd 
is allowed to settle completely. When the whey has 
been separating half an hour, the samples are exam- 
ined for flavor by smelling, after which the whey 
is carefully poured out of the jars and this is re- 



I08 MODERN METHODS OF TESTING MILK 

peated at intervals of 30 to 40 minutes for 8 hours 
or more. Under the favorable conditions of tempera- 
ture, similar to those employed in cheese-making, the 
organisms present develop readily and reveal their 
presence in different characteristic ways. The jars 
are finally opened, any whey present is drained off, 
and the following tests are applied: (i) The curd is 
cut into two pieces. The curd will be solid and free 
from holes on the cut surfaces, if the milk is not 
tainted. If it is spongy and full of holes, it con- 
tains those undesirable organisms that produce gases 
in the curd and injure it for cheese-making, showing 
in the form of "floating curds" and ''huffy" cheese. 
The holes are usually small, their common name be- 
ing "pin-holes." (2) The curd is examined with ref- 
erence to any marked disagreeable odors that may 
be present. Some undesirable organisms reveal their 
presence by smell without making spongy curd. This 
may, perhaps, be best perceived by smelling of a 
freshly cut surface of the curd. Offensive odors are, 
of course, an undesirable indication. Special appara- 
tus for performing the test is furnished by dairy-sup- 
ply houses, but pint fruit- jars and other home-made 
appliances will answer satisfactorily. 

By this method one can learn what particular lot 
of milk among several is responsible for undesirable 
fermentations. ]\Ioreover, having traced the source of 
contamination to a single herd of cows, it is easily 
possible, by applying the test to single cows, to ascer- 
tain which individual or individuals may be the source 
of trouble. 



TESTING THE BACTERIAL CONDITION OF MILK IO9 

Precautions. — Two points must be carefully ob- 
served in carrying out this test : ( i ) The temperature 
must be kept as near 98° F. as possible, in order that 
the bacteria may develop as desired. This can be 
done by keeping the temperature of the water sur- 
rounding the jars at 100° to 102° F. The tempera- 
ture must be v/atched. (2) The thermometer and the 
knife used should be made not only clean but sterile 
each time after using in one sample before placing 
them in another. 

GERBER'S FERMENTATION TEST 

This test consists in heating milk in tubes 6 hours 
at 104° to 106° F. and then observing the odor, ap- 
pearance, taste, etc., for abnormal qualities. The milk 
is heated a second time for 6 hours at 104° to 106° F. 
Any abnormal coagulation of the milk is noticed, such 
as holes due to gas. Gerber states that milk coagu- 
lating in less than 12 hours is abnormal, due either 
to the abnormal character of the milk itself when 
drawn or to improper care after being drawn. Milk 
that does not curdle within 24 to 48 hours is open to 
the suspicion of containing preservatives and should 
be examined for such substances. 

METHOD OF TESTING MILK FOR SUSPENDED 
DIRT 

The amount of dirt in suspension in milk can be 
estimated without serious difficulty. The best way is 
to provide a small centrifugal machine that is made 
to run at higher speed than the Babcock tester. A 



no 



MODERN METHODS OF TESTING MILK 




FIG. 41 — HAND-CENTRIFUGE 
FOR SEDIMENTATION WORK 



form of hand-centrifuge is 
shown in Fig. 41. Special 
graduated tubes (Fig. 42) 
are made to use in this. The 
milk to be tested is stirred 
thoroughly, the tube is filled 
to the highest mark, placed 
in the pocket of the centri- 
fuge and whirled several 
minutes. The sediment col- 
lects at the bottom and can 
be easily measured by read- 
ing the amount on the scale. 
In Fig. 43 is shown a Bausch 
and Lomb electric centrifuge. 
This company also furnishes 
hand-centrifuges capable of 
3,000 to 8,000 revolutions per 





FIG. 42 — TUBE FOR 
SEDIMENTATION WORK 



FIG. 43 — BAUSCH & LOMB 

ELECTRIC CENTRIFUGE 

Speed 1,000 revolutions per minute 



112 



MODERN METHODS OF TESTING MILK 




minute. Their centrifuges and 
tubes can be used also in testing 
for fat in milk by the Babcock 
method. In Fig. 44 is shown 
another form of electrical cen- 
trifuge which is very satisfactory 
for collecting sediments. 

A method less accurate, but 
fairly satisfactory in the absence 
of any better means, is to place about 4 ounces of milk 
in a test-glass (Fig. 45) and let it stand for one or 
two hours. The dirt collects in the bottom and its 
amount can be roughly estimated by the eye. 



FIG. 45 

GLASS FOR COLLECTING 
SEDIMENT IN MILK 



CHAPTER IX 



Methods of Testing! Milk by Rennet- Extract 
and Pepsin 

In cheese-making it is necessary to have some means 
of finding out when the rennet-extract should be ad- 
ded to milk in order to secure the best results in the 
process. This is usually known as "testing the ripe- 
ness of milk." Two methods are in common use for 
this purpose: (i) The Monrad test and (2) the 
Marschall test. 

THE MONRAD TEST 

This test is based upon the amount of time re- 
quired for a definite quantity of milk at a given tem- 




P^IG. 46 — MONRAD RENNET-TEST 

perature to become coagulated by a fixed quantity of 
rennet. 

The pieces of apparatus (Fig. 46) required are the 
following : ( i ) A tin cylinder for measuring milk, 
holding, when full, 160 cc, (2) a 5 cc. pipette, (3) a 

113 



114 MODERN METHODS OF TESTING MILK 

50 cc. glass flask, (4) a thermometer, and (5) a half- 
pint tin basin. 

In testing the ripeness of milk by means of rennet- 
extract, one first prepares a dilute solution of the 
rennet, as follows: One measures with the small pi- 
pette 5 cc. of rennet-extract into the 50 cc. flask. The 
pipette is then rinsed twice with water by sucking it 
full of cold, clean water to the mark, the rinsings also 
being run into the 50 cc. flask. The flask is then filled 
with water to the 50 cc. mark, and the contents are 
well mixed by shaking. The next step is to fill the 
tin cylinder with the well-mixed milk to be tested and 
this is emptied into the half-pint basin. The milk 
must be at the temperature at which one adds the 
rennet in cheese-making, which is generally about 85° 
or 86° F. To the milk at the desired temperature, one 
adds 5 cc. of the diluted rennet solution, mixes it 
through the milk quickly, using the thermometer as 
a stirrer. The exact time when the rennet-extract is 
added to the milk is noted by the second-hand of a 
watch and then again when the milk has coagulated; 
the number of seconds required to coagulate the milk 
is recorded. The exact point of coagulation can be 
seen more sharply by scattering a few particles of 
charcoal (as the blackened end of a partly burned 
match) on the surface of the milk, and then with the 
thermometer starting the surface into motion around 
the dish. The black particles stop the instant the 
milk coagulates. By using a stop-watch, great accu- 
racy and delicacy can be attained. Care should be 
taken to keep the temperature of the milk at 85° or 
86° F., testing frequently with the thermometer; and, 



TESTING MILK BY RENNET-EXTRACT AND PEPSIN II5 



in case the temperature drops, it can be raised by plac- 
ing the basin of milk in warm water. In ordinary 
cheddar cheese-making, milk is ready for the addition 
of rennet when it coagulates in 30 to 60 seconds un- 
der the foregoing conditions. 

THE MARSCHALL TEST 

In this test the same general procedure is followed 
as in the Monrad test, but the rate of coagulation is 
observed in a different way. The following pieces of 
apparatus (Fig. 47) are 
used: (a) A testing cup 
or basin, of about a pint 
capacity, for holding the 
milk to be tested. On the 
inside wall of this cup there 
are graduated spaces be- 
ginning with zero at the 
top and going by half-divis- 
ions to 7 near the bottom 
of the cup, while in the bot- 
tom of the cup is a glass 
tube with a very small bore, 
(b) An ounce bottle with a mark on it to indicate 20 
cc. (c) A spatula for stirring the milk, (d) A i cc. 
pipette. 

The operation of conducting this test is as follows : 
Measure with the pipette i cc. of the rennet-extract 
used and empty it into the ounce bottle, previously 
half filled with clean cold water. Rinse the pipette 
two or three times by drawing water into it from the 
bottle and allowing it to run back into the bottle. Mix 
well by shaking. Then place the milk to be tested 




FIG. 47 

MARSCHALL RENNET-TEST 



Il6 MODERN METHODS OF TESTING MILK 

in the test-cup, setting it in a level position and allow- 
ing the milk to run out at the bottom. Taking the bot- 
tle of diluted rennet in one hand and the spatula in 
the other, watch the level of the milk in the cup. The 
moment the upper surface of the milk drops to the 
zero mark, pour the diluted rennet into the milk and 
stir well. Then leave it alone. When the milk coagu- 
lates, it stops running through the glass tube. From 
the graduated scale, read the number of spaces un- 
covered on the inside of the cup, showing how many 
divisions of milk have run out. The more slowly the 
milk coagulates, the larger the amount that runs out; 
the more quickly the milk coagulates, the smaller the 
amount that runs out and the fewer spaces there are 
uncovered. When about 2^ spaces are uncovered, 
the milk is ready for addition of rennet. The tempera- 
ture must be watched, being tested at the start and 
finish, especially in a cold room. 

Some objectionable features of the Alarschall test 
should be noticed. A difference in the size of the bore 
of the glass tube in the bottom of the cup obviously 
makes a difference in the results. It is found that the 
size of the bore of the glass tubing varies in different 
cups. Therefore, the results given by one cup can not 
be compared with those of another, unless they are 
tested on the same milk and found to agree. Special 
pains must be taken to keep the tube open, since a lit- 
tle dirt quickly stops it. The Marschall test is con- 
venient for ordinary work, but is not capable of as 
great delicacy as is the Monrad test. Results obtained 
by different workers can be compared by the ]\Ionrad 
test, but not by the Marschall test. 



TESTING MILK BY RENNET-EXTRACT AND PEPSIN 11^ 

METHOD OF TESTING RENNET-EXTRACTS 

Rennet-extract is prepared by soaking calves' stom- 
achs in dilute brine. This treatment dissolves from 
the mucous membrane the enzym or chemical ferment 
that has the property of coagulating milk-casein, a 
property upon which the process of cheese-making is 
dependent. The ferment contained in rennet-extracts 
appears to be the same as pepsin in regard to its ac- 
tion upon milk casein. Different brands of rennet-ex- 
tract vary somewhat in their strength, that is, the 
rapidity and completeness with which they coagulate 
milk when used in the same amount. It is therefore 
important to have a means of testing their strength, 
in order that their value may be definitely known and 
that cheese-makers may be able to know in advance 
of using how much they must use for the best results. 
The Monrad and Marschall tests are available for 
this purpose. 

In order to test the comparative strength of differ- 
ent rennet-extracts, one treats different portions of 
the same milk with the different extracts to be tested. 
In all other respects, the details of the methods pre- 
viously given are followed. All conditions must be 
kept alike in the different tests. The strength of the 
rennet-extracts is shown by the rapidity with which 
the milk is coagulated; the stronger the rennet, the 
less the time of coagulation. 

METHOD OF TESTING PEPSIN 

Pepsin is beginning to be used in cheese-making as 
a substitute for rennet-extract. Vivian has worked 
out the important details. The scale-pepsin, of strength 



Il8 MODERN METHODS OF TESTING MILK 

known as 1-3,000, prepared from stomachs of sheep, 
is recommended. It may be used at the rate of 5 
grams for 1,000 pounds of milk. In testing scale- 
pepsin by the rennet test, one can dissolve the scale- 
pepsin at the rate of 5 grams in 4 ounces of water and 
use this solution exactly like a rennet-extract with 
milk. It should be tested in comparison with a sam- 
ple of rennet-extract whose use in cheese-making has 
been tested, the test being made on different portions 
of the same milk. 

TESTING THE AGE OF MILK BY RENNET-TEST 

The age of milks and the care with which they have 
been kept can also be tested in a comparative way by 
the rennet-test, since with the same rennet-extract or 
pepsin solution different milks generally coagulate 
more rapidly in proportion to the amount of acid con- 
tained in them, especially if the amount of lactic acid 
is considerable. 



CHAPTER X 

Methods of Testing Specific Gravity and Solids 
of Milk by the Lactometer 

The specific gravity of milk may furnish important 
information, which becomes of special value when 
taken in connection with the amount of fat present. 
Thus, with the data furnished by the specific gravity 
and the per cent, of fat, we can easily calculate the 
amount of solids in milk and the amount of solids- 
not-fat. 

THE SPECIFIC GRAVITY OF MILK 

Definition of specific gravity. — By the specific grav- 
ity of milk, we mean the weight of a given bulk or 
volume of milk as compared with the weight of an 
equal volume of water at the same temperature. To 
illustrate, suppose we have a vat which, when just full 
of water, contains exactly i,ooo pounds of water at 
60° F. Now, if we fill such a vat full of milk of aver- 
age composition at the same temperature, this amount 
of milk weighs 1,032 pounds. This is so because the 
milk contains, in addition to the water in it, several 
solid substances heavier than water. In this illustra- 
tion we express the relation or ratio of the equal vol- 
umes of water and milk by dividing 1,032 by 1,000; 
the result, 1.032, is the specific gravity of the milk. 

119 



I20 MODERN METHODS OF TESTING MILK . 

Variation in specific gravity of milk. — Since the 
specific gravity of milk largely depends upon the 
amount of solids in it "heavier than water, the specific 
gravity should vary, since we know that the amount 
of solids in milk varies considerably. And so we find 
the specific gravity of some milks below 1.030 and of 
some others above 1.035; ^^t most normal milks from 
herds of cows have specific gravities lying between 
1.030 and 1.034. 

The solids of milk heavier than water are casein, 
albumin and milk-sugar. They constitute the solids- 
not-fat of milk and have a specific gravity of about 
1.500. 

Effect of milk-fat on specific gravity of milk. — 
Milk-fat is lighter than water, its specific gravity be- 
ing about 0.900 compared with that of water as i.ooo. 
Therefore, an increase of fat in milk, relative to the 
other solids, lowers the specific gravity of milk. Thus, 
by adding cream to normal milk, we can r^ake its 
specific gravity lower than that of normal milk. On 
the other hand, by removing fat from milk, we in- 
crease the specific gravity, because we remove what 
is lighter, and leave what is heavier, than water. 

Effect of adding water and other substances to 
milk. — Water being lighter than milk, the specific 
gravity of milk is lowered by addition of water. There- 
fore, it is easily possible by removing cream from nor- 
mal milk to increase the specific gravity and then, by 
adding water, to decrease the specific gravity again 
to that of normal milk. The addition of sugar, salt or 
any similar substance to milk increases the specific 
gravity. Since water has been the most common adul- 



TESTING BY THE LACTOMETER 121 

terant of milk, it was formerly thought that such 
adulteration could readily be detected by ascertaining 
the specific gravity ; but the results of using the spe- 
cific gravity may be very misleading, when consid- 
ered without reference to any other factor. 

INFLUENCE OF TEMPERATURE ON SPECIFIC 
GRAVITY 

Most liquids expand when heated and contract when 
cooled. A vessel full of milk or water at 40° F. will 
overflow when heated considerably higher, that is, 
will hold less of the fluid, and so the same volume 
weighs less at higher than at lower temperatures. 
From this it is readily seen that the specific gravity of 
a liquid like water or milk grows less when its tem- 
perature increases. On the other hand, a vessel full 
of water at 200° F. is not full when cooled to 40° F. 
The same weight of water occupies less volume and 
its specific gravity is higher. Decrease of tempera- 
ture increases the specific gravity of liquids. It is 
therefore necessary in measuring the specific gravities 
of different liquids to have the measurements made at 
the same temperature, if they are to be comparable. 
The temperature commonly used is 60° F. 

METHOD OF TESTING THE SPECIFIC GRAVITY 
OF LIQUIDS 

The specific gravity of liquids is readily measured 
by an instrument known as a hydrometer. The use 
of such an instrument is based on the fact that, when 
a solid body floats in a liquid, it displaces an amount 
of liquid equal in weight to the weight of the floating 



122 



MODERN METHODS OF TESTING MILK 



body. Thus it sinks deeper in a light hquid than in 
a heavy one, because it takes a larger volume of the 
light liquid to equal the weight of the floating body. 
Such an instrument is graduated as the re- 
sult of extensive experiments, so that the 
specific gravity of the liquid in which the 
hydrometer is placed can be read at the 
point where the scale is even with the upper 
surface of the liquid. A hydrometer is cor- 
rect only for the temperature used in stand- 
ardizing it. When a hydrometer has a 
scale specially adapted to the limits of the 
specific gravity of milk, it is called a lactom- 
eter. Of the various lactometers made, only 
two are sufficiently used to deserve atten- 
tion: (i) The Ouevenne, and (2) the New 
York Board of Health, lactometers. 

THE QUEVENNE LACTOMETER 

Description. — This instrument (Fig. 48) 
is a hydrometer the scale of which is di- 
vided into 25 equal parts, going from 15 
to 40. Each division is called a degree, and 
FIG. 48 every fifth degree is numbered on the scale. 
lactoTie-Ter The point marked 15 corresponds to the 
point marked specific gravity 1.015 on an 
ordinary hydrometer, and is the point to which it will 
sink when placed in liquids whose specific gravity is 
1. 01 5. The 40 degree mark on the Ouevenne lactom- 
eter corresponds to the specific gravity 1.040 mark 
on a hydrometer. The relation between specific grav- 



TESTING BY THE LACTOMETER I23 

ity and the scale of the Quevenne lactometer is shown 
as follows : 

SPECIFIC Reading of 

GRAVITY Quevenne lactometer 

1.015 15 

1.020 20 

1.025 25 

1.030 30, 

1.035, etc 35, etc 

Corrections for temperature. — The Quevenne lac- 
tometer is graduated to give correct results at 60° F. 
When it is used in milk, the milk should be at 60° F., 
or, if at some temperature above or below 60° F., a 
correction of the lactometer reading must be made. 
This correction can be closely made by adding to the 
lactometer reading .1 for each degree above 60° F., 
or by subtracting .1 for each degree below 60° F. 
For more exact corrections, consult table on the fol- 
lowing page. 

The Quevenne lactometer should carry a thermom- 
eter, the scale of which is placed for convenience above 
the lactometer scale. 

Process of using Quevenne lactometer. — The sam- 
ple of milk to be tested for specific gravity is brought 
to a temperature between 50° and 70° F. For con- 
venience the milk is placed in a cylinder (Fig. 49), 
which is nearly filled. The lactometer is carefully 
lowered into the milk until it floats and is allowed to 
remain half a minute or more. Then one reads and 
records (i) the point at which the lactometer scale 
comes in contact with the upper surface of the milk; 
and (2) the temperature. The lactometer reading is 





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TESTING BY THE LACTOMETER I25 

then corrected, if the temperature is above or below 
60° F. For example, the lactometer settles in milk, 
which is at a temperature of 65° F., to the point 
marked 29. Adding to the reading for correction .1 
for each degree above 60° F., which in this case is .5, 
the reading becomes 29.5. This means that the spe- 
cific gravity is 1.0295. If the temperature of the 
milk were 55° F., the correction is subtracted and 
the reading becomes 28.5, equal to specific gravity 
1.0285. 

THE NEW YORK BOARD OF HEALTH 
LACTOMETER 

Description. — This lactometer has been in common 
use among milk-inspectors in the east- 
ern and middle states. Its scale is quite 
different from that of the Ouevenne lac- 
tometer, since it is divided into 120 equal 
parts. Beginning at the top of the in- 
strument, the zero point on the scale is 
the point to which the lactometer sinks 
in water; and the point is marked 100 
to which it settles in milk of specific grav- 
ity 1,029 at 60° F. (Ouevenne reading, 
29), the lowest limit supposed to belong 
to normal milk. The distance between 
the zero and 100 points is divided into 
100 equal parts and the scale is then pro- 
longed beyond the 100 mark for 20 di- fig. 49 
visions to 120. The instrument is used cylinder for 
in the same way as the Ouevenne lactom- lactometer 
eter in testing milk. 




126 



MODERN METHODS OF TESTING MILK 



1.000 













1.00S- - 

t.eio- - 

1.015 - 
t.020- - 

I.025' - 


JO- 

*> 

50- 

eo 
;o- 
JO- 

eo' 

100 


" 


15 

?0' 


I 




1.030- - 
).035- 


no 

120- 




35- 
40' 







Comparison o f 
the two lactometer 
scales. — In compar- 
ing the scales of the 
Quevenne and Board 
of Health lactom- 
eters, the following 
points will make clear 
their relations: (i) 
The zero point on 
both instruments in- 
dicates the specific 
gravity of water, 
that is, I. GOO. (2) 
On the B. of H. lac- 
tometer, the 100 di- 
visions or degrees 
from o to 100 corre- 
spond to 29 divisions 
on the Quevenne. 
Therefore one de- 
gree on the B. of H. 
lactometer c o r r e- 
sponds to .29 degree 
on the Quevenne. To 
convert the B. of H. 
lactometer reading 
into that of the 
Quevenne, multiply 
the reading of the 
former by .29. The 
relation of the specific gravity scale of a hydrometer 



FIG. 50 — COMPARISON OF DIFFERENT 

SPECIFIC GRAVITY SCALES 
.S is specific gravity scale; A^is New York 
Board of Health lactometer; Q is 
Quevenne lactometer. 



TESTING BY THE LACTOMETER 



127 



to the scales of the Ouevenne and B. of H. lactometer 
is shown in Fig. 50. 



TABLE II. — DEGREES ON QUEVENNE LACTOMETER CORRESPONDING TO 
DEGREES ON NEW YORK BOARD OF HEALTH LACTOMETER 



BOARD OF 




BOARD OF 




BOARD OF 




HEAIvTH 


QUEVENNE 


HEALTH 


QUEVENNE 


HEALTH 


QUEVENNE 


Degrees 


Degrees 


Degrees 


Degrees 


Degrees 


Degrees 


GO 


17.4 


81 


23.5 


101 


29.3 


61 


17.7 


82 


23.8 


102 


29.6 


62 


18.0 


83 


24.1 


103 


29.9 


63 


18.3 


84 


24.4 


104 


30.2 


64 


18.6 


85 


24.6 


105 


30.5 


65 


18.8 


86 


24.9 


106 


30.7 


66 


19.1 


87 


25.2 


107 


31.0 


67 


19.4 


88 


25.5 


108 


31.3 


68 


19.7 


89 


25.8 


109 


31.6 


69 


20.0 


90 


26.1 


110 


31.9 


70 


20.3 


91 


26.4 


111 


32.2 


71 


20.6 


92 


26.7 


112 


32.5 


72 


20.9 


93 


27.0 


113 


32.8 


73 


21.2 


94 


27.3 


114 


33.1 


74 


21.5 


95 


27.6 


115 


33.4 


75 


21.7 


96 


27.8 


116 


33.6 


76 


22.0 


97 


28.1 


117 


33.9 


77 


22.3 


98 


28.4 


118 


34.2 


78 


22.6 


99 


28.7 


119 


34.5 


79 


22.9 


100 


29.0 


120 


34.8 


80 


23.2 











128 MODERN METHODS OF TESTING MILK 

Corrections for temperature. — In using the B. of 
H. lactometer, correction is made for temperatures 
above or below 60° F. For each degree of tempera- 
ture of milk above 60° F., add .3 to the lactometer 
reading, and for each degree below 60° F. subtract .3 
from the reading. 

PRECAUTIONS IN TESTING SPECIFIC GRAVITY 
OF MILK 

1. Milk should, for best results, not be examined 
until I to 2 hours or more after milking, since the 
specific gravity of milk is lower for a while after be- 
ing drawn than it is later, due chiefly to the presence 
of gases. 

2. The sample of milk must be completely mixed. 

3. The lactometer must be kept clean. 

4. In milk which has been preserved by potassium 
bichromate, the specific gravity is about one degree 
higher than in the normal milk, in case the usual 
amount of bichromate has been added. (See p. 30). 

VALUE OF LACTOMETER IN DETECTING ADUL- 
TERATED MILK 

The value of the lactometer in detecting adulterated, 
especially watered, milk was formerly overestimated. 
Taken alone, the results given by the lactometer may 
be thoroughly unreliable and misleading. It has 
come to be quite generally recognized that the proper 
use of the lactometer in milk inspection is largely to 
indicate whether a sample is suspicious and to furnish 
a guide as to whether it is necessary to take a sam- 
ple for further detailed investigation by chemical anal- 



TESTING BY THE LACTOMETER I29 

ysis. As already stated, a milk which is both skimmed 
and watered may appear to be entirely normal by the 
lactometer. 

METHOD OF TESTING MILK FOR SOLIDS BY 
LACTOMETER 

As the result of extended studies of the relations ex- 
isting between the specific gravity of milk, milk-fat 
and milk-solids, rules have been formulated by means 
of which it is possible to calculate with a close degree 
of approximation the total solids of milk, when one 
knows the percentage of fat and the (Ouevenne) lac- 
tometer reading. 

Babcock's formulas for solids and solids-not-fat. — 
The following formulas were devised by Dr. Bab- 
cock: 

(i) Formula for determining solids-not-fat. — Sol- 
ids-not-fat=^L+.2f, in which L is the reading of 
the Quevenne lactometer and f is the per cent, of fat 
in the milk. 

(2) Formula for determining solids in milk. — Total 
soHds==i4L+i.2f. 

These formulas can be expressed in the form of 
rules as follows : 

Rtde I. — To find the per cent, of solids-not-fat in 
milk, divide the reading of the Quevenne lactometer 
by 4, and to the result add the per cent, of fat in the 
milk multiplied by .2. 

Ride 2. — To find the per cent, of solids in milk, di- 
vide the Quevenne lactometer reading by 4, and to 
the result add the per cent, of fat multiplied by 1.2. 
Examples: — A milk containing 4 per cent, of fat 



130 



MODERN METHODS OF TESTING MILK 



I 




shows a lactometer reading of 32. What 
T^a s| I is the per cent, (a) of soHds-not-fat, (b) 
^ "^ - of total solids? 

(a) The lactometer reading (32), di- 
vided by 4, equals 8. The per cent, of 
fat (4), m'ultiplied by .2, equals .8. Add- 
ing 8 and .8, we obtain 8.8 as the per 
cent, of solids-not-fat. 
-ii°li"' b) The per cent, of total solids in the 

milk is 12.8 per cent.; for the lactometer 
reading, divided by 4, equals 8, the per 
cent, of fat (4) multiplied by 1.2 equals 
4.8, and 8 plus 4.8 equals 12.8. 

Richmond's slide-rule for calculating 
solids. — Instead of going through the 
details of calculation to estimate solids 
in milk, Richmond uses a slide-rule which 
is a clever mechanical calculating device. 
(Fig. 51). The results obtained in this 
manner agree closely with those given by 
Babcock's formulas. The method of 
using the slide-rule is as follows : De- 
termine (i) the Quevenne lactometer 
reading, (2) the temperature of the 
milk, and (3) the per cent, of fat in the 
-pBi' milk. Then set the central slide of the 
^v^m-\ W j.^|g gQ ^i^^^ ^j^g observed lactometer read- 
ing is opposite the 60 degree (tempera- 
ture) mark. The true lactometer read- 
ing is found opposite the line indicating 
the observed temperature of the milk. Having thus 
corrected the lactometer reading for temperatures 



FIG. 51 
Richmond's 
slide-rule 



TESTING BY THE LACTOMETER I3I 

Other than 60° F., next set the arrow on the sUding 
portion of the rule opposite the per cent, of fat found 
in the milk and read the total solids contained in the 
milk corresponding with the corrected lactometer read- 
ing or specific gravity. 

To illustrate, suppose the lactometer reading of a 
sample of milk, at 70° F. is 30 and the per cent, of fat 
is 4. To correct for temperature and find what the 
lactometer reading would be at 60° F., the lactometer 
reading (30) is placed opposite the little arrow at 60 
on the temperature scale. Then, looking at the point 
of temperature 70, we find opposite this point 31.3, 
■which is the corrected or true reading. Next, we 
place the arrow opposite the 4 per cent, mark, as the 
milk contains 4 per cent, of fat, and then notice where 
the point 31.3 (specific gravity), comes in contact with 
the solids scale. It corresponds closely to 12.8, which 
is the per cent, of total solids in the sample of milk 
examined. Some practice with this slide-rule enables 
one to work rapidly. 

Specific gravity of milk-solids. — The following rule 
has been proposed by Fleischmann for calculating the 
specific gravity of milk-solids: Multiply the specific 
gravity of the milk by 100, from the result subtract 
100 and divide this result by the specific gravity of 
the milk. Subtract the last result from the per cent, 
of total solids in the milk and then divide by this re- 
sult the per cent of total solids of the milk. This may 
also be expressed by the following formula: 

milk-solids 



Sp. gr. milk-SOlids=niilk-solids— (looXsp. gr.)— 100 

sp. gr. 



132 MODERN METHODS OF TESTING MILK 

Example: A sample of milk contains 12.5 per cent, 
of solids and has a specific gravity of 1.031; 
— what is the specific gravity of the milk-solids? 

100 X I.O'^I 100 r ^ 12. =5 ^ 

■ = 3-oo6; 12.5—3.006 = 9.494; —^==1.32 

1.031 ^ "" ^^^^ 9.494 

This calculation may assist in determining whether 
a sample of suspected milk has been adulterated. The 
variations of the specific gravity of milk-solids is slight, 
ranging between 1.25 and 1.34. Milks richer in fat 
have solids of lower specific gravity. The specific 
gravity of milk-solids is not changed by watering milk, 
but is increased by removing fat or by addition of 
skimmed milk. Hence, milk whose solids have a 
specific gravity above 1.34 is suspected of being 
skimmed, while a specific gravity above 1.40 is re- 
garded as clear evidence of skimming. 



CHAPTER XI 

Methods of Testing Milk and Milk Products 
for Adulterations 

Milk is commonly adulterated in one of the follow- 
ing ways: (i) By addition of water, (2) by removal 
of fat (skimming) or addition of skim-milk, (3) by 
addition of substances not normally found in milk, 
such as preservatives and coloring matter. All these 
forms of adulteration may occur in the same milk. 

DETECTION OF ADDED WATER IN MILK 

Since water in milk is the same chemical compound 
as the water found everywhere else, it is impossible 
to identify added water in milk by any direct test for 
special properties. The presence of added water in 
milk can be learned with certainty only by indirect 
means and even then not with certainty in all sus- 
pected cases. An examination of milk direct from 
the cow or herd, when this is possible, may settle the 
question of watering. The lactometer, while unrelia- 
ble as a sure means of detecting added water in milk, 
may give a helpful suggestion, used as a preliminary 
test. Thus, if a milk shows a specific gravity under 
1.028, it is open to the suspicion of being watered, and 
should then be carefully examined in other ways. 

Most states fix legal standards for the per cent, of 
water, solids, fat, and solids-not-fat in milk, and any 

133 



134 MODERN METHODS OF TESTING MILK 

milk falling below the fixed limit in composition is 
regarded as adulterated. Thus, a standard common 
to several states is 12 per cent, of solids and 3 per cent, 
of fat. This means also that such legal-standard milk 
must not contain more than 88 per cent, of water or 
less than 9 per cent, of solids-not-fat. 

The relations of the different constituents of milk 
have been studied and formulas have been devised 
which enable one in an approximate way to tell how 
much water has been added to a sample of milk be- 
yond the amount allowed by the standards. These 
formulas are based on the assumption that the limits 
fixed by the legal standard represent the lowest 
amounts of solids and fat found in normal milk, and 
they are correct only when the original milk contains 
the lowest percentages given in the legal standard. 

In calculating the amount of added water in milk, 
the amount of solids-not-fat (total solids minus fat) 
is used as a basis. The procedure is as follows : 

(i) Determine the per cent, of fat in the suspected 
sample. 

(2) Take the lactometer (Quevenne) test. 

(3) Determine the amount of solids-not-fat ac- 
cording to the formula, 34L+.2f. (p. 129). 

(4) Apply the following rule: Multiply the per cent, 
of solids-not-fat by 100 and divide the result by the 
legal standard for solids-not-fat. Subtract the last 
result from 100 and the result is the per cent, of ad- 
ded water in the sample of suspected milk. This rule 
is expressed in the form of the following formula: 

^ . r J ^ J . per cent, of solids-not-fat X loo. 

Per cent, of added water=ioo— , — , — 7 3 s-i r^ nr^z 

legal standard for sohds-not-fat. 



TESTING MILK FOR ADULTERATIONS I35 

This formula gives only the amount of water 
added beyond the limit fixed by the legal standard 
and is correct only if the original milk contained the 
amount of solids-not-fat prescribed by the standard 
(usually 9 per cent.). Hence, in cases of watered 
milk, the calculated amount of water added is gener- 
ally less than the real amount added. 

Example : A milk is found to contain 3 per cent, of 
fat and to show a lactometer reading of 27. Applying 
the formula for finding the amount of solids-not-fat, 
the per cent, is 7.35. If the legal standard for solids- 
no t- fat is 9, then the formula becomes 

ioo-'-^|^i^°=i8.3, 

the per cent, of added water that is contained in the 
milk, assuming that it contained 9 per cent, of solids- 
not-fat before being watered. 

The following rule can also be used : Add together 
the lactometer reading and the per cent, of fat present 
in the milk, divide the sum by 36, multiply the result 
by TOO and subtract the last result from 100. Ex- 
pressed as a formula, this becomes 

Per cent, of 1 • .„ lactometer reading +per cent, of fat \/ 
added water r"" ^^1^=1°° ^6 XlOO. 

An examination of the serum of milk by means of 
a refractometer gives, probably, the most reliable 
means of detecting added water in milk, but this 
method is available only for special workers. For its 
details see "Food Inspection and Analysis," by Leach, 
(P- 139)- 



136 MODERN METHODS OF TESTING MILK 

DETECTION OF SKIMMED MILK 

The percentage of fat in milk in relation to the 
other milk-solids is reduced either (i) by direct re- 
moval of fat through some process of skimming or 
(2) by the addition of separator skim-milk to nor- 
mal milk. Milk containing less than 3 per cent, of 
fat is generally skimmed. Watering milk does not 
disturb the relations of the constituents of milk to 
one another, since it reduces the percentages of all 
uniformly, but the removal of fat does very seriously 
affect the amounts of the constituents in respect to 
their relative percentages. In skimming milk, the 
solid constituent most largely removed is fat, com- 
paratively little casein, sugar, etc., being taken with 
the fat. The removal of fat therefore leaves the milk 
containing less fat but with most of its casein, sugar, 
etc., still remaining. In normal herd milk, containing 
over 3 per cent, of fat, the percentage of fat is rarely 
as low as the percentage of casein and albumin. In 
5,500 analyses of samples of American milks, compiled 
by the author, with a fat content lying between 3 and 
5 per cent., the fat averages 3.92 per cent, and the ca- 
sein and albumin together, 3.20 per cent. ; that is, for i 
part of casein and albumin there is an average of 
1.225 parts of fat. In skimming such milk, the fat may 
be decreased to i per cent, or .1 per cent., but the re- 
maining milk still contains about 3.20 per cent, of 
casein and albumin. Milk is open to the suspicion of 
being skimmed, when the percentage of fat falls be- 
low that of the casein and albumin. 

The percentage of fat removed, based on the legal 



TESTING MILK FOR ADULTERATIONS 1 37 

standard, may be calculated by the following rule: 
Multiply the per cent, of fat in the milk by loo, di- 
vide the result by the legal standard for fat and sub- 
tract this from lOo; or expressed as a formula: 

The per cent, of fat removed=ioo — ^^ ^°° This 
formula is true only for milks originally containing 3 
per cent, of fat and so its results are generally much 
below the truth. For example, in a milk containing 
originally 5 per cent, of fat, which has been skimmed 
to 2.50 per cent., thus removing 50 per cent, of the 
fat in the milk, the above formula would indicate that 
only 16.6 per cent, of the fat had been removed. In 
most cases results nearer the actual truth are given 
by substituting 3.75 for 3 in the formula. 



GENERAL METHOD FOR JUDGING WATERED 
AND SKIMMED MILK 

Having found in a sample of milk ( i ) the per cent, 
of fat, (2) the specific gravity of the milk and (3) of 
the milk-sohds, (4) the per cent, of solids, and (5) of 
solids-not-fat, one may arrive at fairly safe conclu- 
sions in regard to the watering and skimming by 
making comparison with the percentages of constitu- 
ents present in average normal milk. In forming such 
conclusions, the following facts should be kept in 
mind : 

1. Water has a. lower specific gravity than milk. 

2. Watering milk decreases (a) the lactometer read- 
ing, (b) the fat, (c) total solids, and (d) solids-not-fat. 

3. Water has a higher specific gravity than milk-fat. 



138 MODERN METHODS OF TESTING MILK 

4. Skimming milk (a) increases the lactometer read- 
ing, (b) decreases the fat and total solids, (c) slightly 
increases the solids-not-fat, and (d) increases the spe- 
cific gravity of the milk-solids. 

5. Skimming and watering decrease all constituents, 
but lower the fat more in proportion than the solids 
and solids-not-fat. 

, 6. Skimming and watering may produce the same 
specific gravity as in normal milk. 

7. The amount of fat in milk is more variable than 
the amount of solids-not-fat. 

8. Herd milk which shows a lactometer reading 
above 33.5, along with a low percentage of fat, and a 
specific gravity of solids above 1.40, can be regarded 
as skimmed. 

9. Herd milk showing a lactometer reading below 
28 may be regarded as watered, especially with low 
fat, solids and solids-not-fat. 

Milk is watered when (i) the specific gravity of 
the milk is low, (2) the percentage of fat and solids- 
not-fat is low and (3) the specific gravity of the milk- 
solids is between 1.25 and 1.35. 

Milk is skimmed when (i) the specific gravity of 
the milk and of the milk-solids is high; when (2) 
the per cent, of solids-not-fat is high, and when (3) 
the per cent, of fat and solids is low. 

Milk is watered and skimmed when (i) the spe- 
cific gravity of the milk is normal or otherwise, (2) 
the specific gravity of the milk-solids is normal or high, 
and (3) the per cent, of fat and solids-not-fat is low. 



TESTING MILK FOR ADULTERATIONS 1 39 

DETECTION OF FOREIGN SUBSTANCES IN MILK 

The foreign substances most frequently found in 
milk are preservatives and coloring matters. The pre- 
servatives in common use are formalin, boric acid, 
borax and sodium bicarbonate. The coloring matters 
generally used are annatto and coal-tar dyes (azo- 
colors), which are added to milk to make it look rich, 
and, especially in case of skimmed and watered milk, 
to cover up the signs of such adulterations. 

Test for annatto. — To lo cc. of milk in a test-tube 
add 10 cc. of ether, shake vigorously and let stand un- 
til the ether separates on top of the milk. If annatto 
is present, the layer of ether will be yellow, the depth 
of color depending on the amount of annatto present. 

Test for Coal-Tar Dyes. — The azo-colors, which 
are the ones most commonly used in coloring milk, may 
be detected by adding lo cc. of milk to lo cc. of strong 
hydrochloric acid and mixing, when a pink coloration 
appears. 

Tests for Formalin. — Formalin, which is a 40 
per cent, solution of formaldehyde, is commonly di- 
luted and sold under such names as "Freezine," "Ice- 
line," etc., which contain from 2 to 6 per cent, of for- 
maldehyde. In making the Babcock test in milk, the 
presence of formalin may be shown when a marked 
violet layer forms at the junction of the acid and milk 
just after pouring the acid into the test-bottle. The test 
may also be performed by taking 10 cc. of milk in a 
test-tube or Babcock test-bottle, and adding about 5 
cc. of sulphuric acid, such as is used in the Babcock 
test, pouring the acid down the side of the tube so 
that it does not mix with the milk. 



140 MODERN METHODS OF TESTING MILK 

Leach's test, which is more deHcate, is performed 
as follows: Make a solution of hydrochloric acid (spe- 
cific gravity 1.2) containing 2 cc. of 10 per cent, ferric 
chloride per liter. Add 10 cc. of this solution to 10 
cc. of milk in a white teacup and heat slowly over a 
flame to boiling, giving the cup a rotary motion. If 
formalin is present, a violet coloration appears, vary- 
ing in depth with the amount present. 

Test for borax and boric acid. — To 25 cc. of milk 
add lime water, until the milk is alkaline, evaporate to 
dryness and burn to an ash in a small porcelain or 
platinum dish. To the ash add a few drops of dilute 
hydrochloric acid, not too much ; then add a few drops 
of water and place in this water solution a strip of 
turmeric-paper (obtainable at drug-stores). Then dry 
the paper, when a cherry-red color will appear on the 
paper if either borax or boric acid is present. This test 
is made still more certain by moistening the reddened 
paper with a drop of an alkali solution, when the pa- 
per turns to a dark-olive color in the presence of borax 
or boric acid. 

Test for sodium carbonate. — To 10 cc. of milk add 
10 cc. of alcohol and a few drops of a i per cent, so- 
lution of rosolic acid. Carbonates are present if a 
rose-red color appears, while pure milk shows a brown- 
ish-yellow color. 

ADULTERATIONS OF CREAM 

The adulterants of cream are the same as those for 
milk and are detected in the same manner. Gelatine 
and sucrate of lime are used to some extent to give 
cream a greater consistency. 



TESTING MILK FOR ADULTERATIONS 141 

ADULTERATIONS OF BUTTER 

The most common adulteration of butter is substi- 
tution, in part or in whole, of fat other than butter- 
fat, such as products from beef-fat and lard. Occa- 
sionally preservatives are found, such as occur in milk. 
"Renovated" or ''process" butter is made from refuse 
butter that can not be disposed of otherwise on the 
market. Excessive water or casein should be regarded 
as an adulteration. Harmless coloring matter has been 
universally allowed. The absolute identification of 
such adulterants as oleomargarin requires somewhat 
elaborate chemical methods. Only simple tests can 
be given here. 

Foam-test for oleomargarin and "renovated" but- 
ter. — Melt in an ordinary tablespoon a piece of the 
suspected butter about the size of a small chestnut, 
holding it over a small flame, — a candle flame will do. 
Stir the fat, while melting, with a match or similar 
stirrer. Then lower the spoon into the flame and let 
the fat boil vigorously, stirring thoroughly several 
times during the boiling and not neglecting the outer 
edges. Oleomargarin and "renovated" butter boil 
with marked noise, sputtering more or less and pro- 
ducing little or no foam. Genuine butter generally 
boils with much less noise and foams up vigorously. 

Milk-Test for oleomargarin. — In a tin measuring- 
cup take about one gill of sweet milk or water, heat 
to about 140° F. and then add a slightly rounded tea- 
spoonful of the suspected sample. Stir with a small 
piece of wood, about the size of a match or smaller, 
until the fat is melted. Then immerse the cup to about 
one-third of its height in a pan of water in which there 



142 MODERN METHODS OF TESTING MILK 

are several large pieces of ice. Stir the liquid contin- 
uously, alternating a circular and crosswise motion, 
until the fat hardens, when it can be easily collected 
into one lump by means of the wooden stirrer, if it is 
oleomargarin ; but, if butter, the fat will form little 
granules and can not be collected in one lump. When 
milk is used in the test, it should contain as little fat 
as possible. In this test "renovated" butter behaves 
like genuine butter. 

ADULTERATIONS OF CHEESE 

Only two kinds of adulteration are common in 
American cheddar cheese : ( i ) The removal of fat in 
varying degrees producing so-called skim-cheese, and 
(2) the use of fat other than milk-fat, producing the 
so-called filled cheese. Harmless coloring matter is 
allowed. Cheese containing less than 32 per cent, of 
fat can be regarded as having been made from milk 
containing less than its normal amount of fat. The 
per cent, of fat in filled cheese is generally lower than 
in cheese made from normal milk. 



CHAPTER XII 

The Babcock Test Applied to Farm Conditions 

The Babcock test finds application on the farm of 
every dairyman in one or more of the following ways : 

i) In testing the quality of milk in respect to fat 
produced by individual cows and by the herd. 

(2) In testing cream. 

(3) In testing skim-milk. 

(4) In testing buttermilk. 

(5) In testing milk and cream as a means of self- 
protection. 

TESTING COWS 

The most effective test of the value of a dairy cow 
is the production of milk and of milk-fat. Evidence 
has been carefully collected showing that many cows 
in this country are kept at an actual loss. The 
owners of such cows may be conscious of the fact 
that they are not prospering, but without having any 
idea of the cause. The amount of fat in milk required 
for various purposes differs somewhat. For ordi- 
nary market purposes, where consumers take as a 
matter of course any kind of milk delivered to them, 
the most profitable cow is the one producing a large 
yield of milk, which generally means a low percentage 
of fat, frequently just enough to keep above the legal 
standard. The statement applies to milk sold by bulk 

143 



144 MODERN METHODS OF TESTING MILK 

or by weight alone, whether sold for direct consump- 
tion or taken to a cheese-factory or creamery. But 
whenever milk is paid for according to its percentage 
of fat, as in certain forms of market milk, at cream- 
eries, at condenseries, and at progressive cheese-fac- 
tories, the cow producing the largest amount of milk- 
fat will nearly always be found the most profitable. 
As a rule, a pound of milk-fat can be produced at less 
cost in rich milk than in poor milk. The only method 
of ascertaining accurately the value of a cow or of a 
herd for the production of milk- fat is by testing the 
milk. The real object of a test is to find the total num- 
ber of pounds of fat produced in the milk for a defin- 
ite period of time, the most satisfactory unit being one 
period of lactation, that is, from the time of calving 
to the time of becoming dry. 

In testing the value of a cow for the production of 
milk-fat, two factors must be considered: (i) The 
amount of milk produced and (2) the per cent, of fat 
in the milk. The first amount is obtained by weigh- 
ing the milk, and the second by testing the milk by 
the Babcock test. From these data the amount of 
milk-fat produced is easily found. 

In applying the Babcock test on the farm to indi- 
vidual cows, certain details need to be considered, 
such as (i) the duration of the testing, (2) the fre- 
quency of testing, (3) the method of sampling, (4) 
weighing the milk, (5) keeping records, and (6) cal- 
culating results. In carrying out the work of the 
milk-test, all necessary details are given in Chapter 

IV, p. 53- 

Duration of testing. — For best results, the tests 



FARM CONDITIONS I45 

should be made at intervals for a whole period of lac- 
tation. 

Frequency of testing. — It is not practicable to test 
the milk of every milking for fat and it is not neces- 
sary. On the other hand, the testing of a single milk- 
ing or of a day's milk or even of a week's milk is in- 
sufficient, since, for many reasons, the percentage of 
fat may vary greatly from one time to another. The 
following plan combines a high degree of accuracy 
with the least amount of labor: Make the first fat- 
test in about two weeks after the cow calves and then 
repeat it regularly once in two weeks during the period 
of lactation. Even a monthly testing will, however, 
give fairly accurate results. 

Method of sampling. — When a single cow's milk 
is to be tested, the following precautions should be 
observed in taking the sample : 

( I ) The cow must be milked dry at the milking pre- 
vious to the one to be tested. (2) On the day of milk- 
ing for the test, the cow is milked as completely as 
possible each time. (3) After the morning's milk- 
ing, the milk is well mixed by pouring from one pail 
to another or by stirring with a dipper, and about a 
gill is at once dipped out and poured into a pint fruit- 
jar, which has been thoroughly cleaned and scalded. 
The sample is kept in a cool place. Repeat the samp- 
ling with the evening's milk or with each milking, if 
the cow is milked more than twice a day, adding a sam- 
ple of each to the jar containing the morning's milk. 
(4) Make a test before the milk can sour, mixing well 
before taking samples for the test by pouring back 
and forth a few times from one vessel to another. If 



146 MODERN METHODS OF TESTING MILK 

it is impossible to make the test promptly, add bi- 
chromate of potash to preserve the sample, as directed 
on p. 30. (5) In testing the milk of several cows at 
the same time, label each sample- jar with the number 
or name of the cow furnishing the milk. (6) If the 
milk is to be tested also for solids by the lactometer, 
take about a half -pint sample from each milking. 

More strictly accurate results are secured if each 
milking is sampled by a tube, as stated on p. 27. 

Weighing milk. — In testing a cow, the milk must 
always be weighed on the testing day immediately af- 
ter the milking is completed. As it is so easy to weigh 
milk, it is desirable to weigh the milk at every milking, 
or, at least, on two or three days each week. Accurate 
spring scales of moderate cost are available. 

Keeping records. — Records of each cow tested 
should be carefully kept, the following facts being re- 
corded: (i) Date, (2) name of cow, (3) pounds of 
milk given, (4) per cent, of fat in milk, (5) lactometer 
reading, if desired. 

Calculating results. — The following data can be de- 
rived by calculation from the facts recorded above: 
(i) Pounds of fat produced on day of test, (2) pounds 
of fat and milk produced each month, (3) pounds of 
fat and milk produced for one period of lactation. 

The amount of fat on the day of the test is found 
by multiplying the total number of pounds of milk 
given by the per cent, of fat found and dividing by 
100. For example, if the day's yield of milk is 25 
pounds and the per cent, of fat is 4, the day's milk 
contains i pound of milk-fat. (See p. 185). 

The amount of milk and fat produced each month 



FARM CONDITIONS I47 

is found as follows, when the test is made once in two 
weeks : Add the daily yields of milk for the day of 
the test and for one week before and one week after 
the test, thus obtaining the milk yield for 15 days. 
Multiply this sum by the per cent, of fat found on the 
day of the test and the result is the fat yield for half 
a month. This added to the next half month gives the 
yield of fat for the month. 

The monthly yields of milk and fat, added together 
at the end of the period of lactation, give the total 
yields for the period. 

APPLICATION OF RESULTS OF TESTING INDI- 
VIDUAL COWS 

A progressive dairyman will discard from his herd 
any animal that can not produce, at least, 200 pounds 
of milk- fat in a year, especially if the milk is sold on 
the basis of its fat content; and he will aim, by means 
of intelligent breeding, feeding and care, to increase 
the annual yield of milk-fat to 250 or 300 pounds for 
each cow. 

TESTING CREAM ON THE FARM 

There are several conditions under which it is of 
advantage to test cream on the farm in order to know 
its fat content. 

When a dairyman is producing cream to sell directly 
to consumers, it is important to know its percentage 
of fat, in order that it may be uniform from day to 
day, whatever the desired percentage may be. The 
work of the cream-separator may be controlled ad- 



148 MODERN METHODS OF TESTING MILK 

vantageously only by knowing the percentage of- fat 
in the cream produced. In states where a certain per- 
centage of fat in cream is required by law, it is im- 
portant for the dairyman to know that his product is 
up to standard before he sells it. 

In making butter on the farm, better results can 
be secured by having the cream of a uniform rich- 
ness in fat, and the percentage of fat in cream can 
be accurately known and regulated only by testing. 

TESTING SKIM-MILK AND BUTTERMILK ON 
THE FARM 

The completeness with which fat is removed from 
milk by different methods of creaming, whether by 
separator or by gravity processes, can be known accu- 
rately only by testing the skim-milk for its fat content. 
With the knowledge furnished by testing, one is in 
position to prevent further losses when they are known 
to exist. Similarly, the efficiency of churning may be 
found by testing the buttermilk for its fat content. 

TESTING MILK AND CREAM FOR SELF- 
PROTECTION 

When dairymen sell milk or cream to milk-dealers, 
creameries, cheese-factories, shipping-stations, con- 
denseries, etc., on the basis of the per cent, of fat in 
milk, it is often a matter of satisfaction to know that 
the tests which serve as a basis of payment are cor- 
rect. If a dairyman will take pains to acquire the skill 
necessary to perform the operations of the Babcock 
test, he can satisfy himself easily in regard to the ac- 



FARM CONDITIONS 1 49 

curacy of the tests of his milk made by others. In 
cases where a purchaser reports the test lower than 
it is, his dishonesty can be detected by means of home 
testing. 

It is also important for the dairyman who sells milk 
directly to consumers to know that his milk is above 
the legal standard. Much annoyance and expense may 
sometimes be saved by knowing the percentage of fat 
and solids in the milk one sells. 



CHAPTER XIII 

Methods of Commercial Testing^ and Scoring 
of Butter and Cheese 

In commercial transactions in butter and cheese, 
certain points or qualities have been adopted as a basis 
or standard in judging the commercial value of these 
products. The terms used in expressing the different 
qualities vary considerably in different market cen- 
ters, and the same expression is used with different 
meanings by different persons. Frequently individ- 
uals use terms that are strictly local or personal. It 
is desirable that there should be a uniform usage and 
a common understanding in respect to the terms used 
in judging dairy products. The attempt is made here 
to discuss the terms in common use and to define them 
as well as may be, in the hope that it may serve as a 
beginning in bringing about a general agreement in 
respect to the use and understanding of the expres- 
sions employed in testing and scoring dairy products. 
The definitions here given can hardly be expected to 
be in full agreement with the usage of everyone, since 
individuals differ from one another so much in their 
use of these terms. 

SAMPLING AND TESTING BUTTER 

In obtaining a sample of butter from a package for 
examination, a butter-trier (Fig. 52) is used. This 
is inserted its whole length, if possible, into the but- 

150 



Q 



COMMERCIAL TESTING OF BUTTER AND CHEESE I5I 

ter, turned around once and then drawn out, bringing 
with it a long, round plug as a sample„ The plug, as 
soon as drawn, is examined for flavor by smelling and 
next by tasting. It is then broken across 
to examine the grain or texture, and then 
other qualities are examined in turn. 

TERMS USED IN DESCRIBING 
QUALITIES OF BUTTER 

The qualities that have been selected 
to serve as a basis or standard in the 
commercial testing and scoring of but- 
ter are as follows: (i) Flavor, (2) tex- 
ture, (3) body, (4) moisture, (5) color, 
(6) salt and (7) appearance. 

Flavor. — By flavor is meant the qual- 
ity that is perceptible to the senses of 
smell and taste. The sense of smell is, 
as a rule, capable of being developed so 
as to be more highly sensitive than the 
sense of taste in detecting variations of 
flavor. The flavor in normal butter is 
due to the formation of certain organic 
compounds in minute quantities during 






the cream-ripenmg- process. What spe- ^ 

.- 1 1 1 BUTTER TRIER 

cinc compounds these are has not yet 

been learned. The odor is not that of lactic acid, 

since that is odorless. 

Testing Flavor. — The flavor is obtained by placing 
the plug of butter under the nose as soon as possible 
after the plug is drawn. A portion of the butter is 
also tasted. 



152 MODERN METHODS OF TESTING MILK 

Terms describing flavors. — The following terms 
are selected from the great variety of names that are 
applied to various flavors found in butter: (i) Per- 
fect, (2) quick, (3) clean, (4) light, (5) buttermilk, 
(6) rancid, (7) tallowy, (8) cowy, (9) fishy, (10) 
tainted, (11) stable, (12) weedy, (13) cheesy. 

(i) Perfect flavor applies to butter which possesses 
the characteristic aroma and taste of high-grade but- 
ter in a well-marked degree. It is difficult to de- 
scribe this flavor adequately, but it is commonly char- 
acterized as nutty, clean, pleasantly aromatic, delicate 
and sweet. Perhaps the best description of it is to 
liken it to the flavor of clean, well-ripened cream. It 
should be entirely free from rancidity or any unusual 
flavor. 

(2) Quick flavor is so delicate and volatile that it 
disappears quickly; "high" is also applied to the same 
condition. 

(3) Clean flavor is free from every trace of unpleas- 
ant aroma or taste. 

(4) Light or flat flavor in butter indicates absence of 
marked flavor, due to lack of cream-ripening, to ex- 
cessive washing of granules and to other conditions. 

(5) Buttermilk flavor is somewhat sour in taste and 
like buttermilk in aroma. It is due to the presence of 
an excessive amount of buttermilk in the butter. 

(6) Rancid flavor is that of butyric acid, the pres- 
ence of which is due to the use of over-aged cream or 
milk or to age of butter, in which butyric acid fer- 
mentation has occurred. When the flavor is strong, 
it produces an unpleasant, strangling or choking sen- 
sation in a sensitive throat. The odor is very pene- 
trating and lasting. 



COMMERCIAL TESTING OF BUTTER AND CHEESE I53 

(7) Tallozvy flavor is like that of tallow. 

(8) Cozvy flavor refers to the animal odor, particu- 
larly as noticed in the breath of a cow. It appears to 
be especially prominent in cows freshly turned into 
pasture. 

(9) Fishy odor is rather suggestive of salted cod- 
fish. It is usually due to a special form of fermentation 
appearing in the milk and cream. 

(10) Tainted flavor covers a variety of odors and 
tastes that are offensive in varying degrees. 

(11) Stable flavor is the one characteristic of cow 
manure. 

(12) Weedy flavor includes such abnormal flavors as 
may come from onions, leeks, cabbages, turnips, etc. 

(13) Cheesy flavor suggests the flavor of cheese and 
is due to fermentation changes in the proteid of but- 
ter; it is more common in unsalted butter. 

Texture. — The texture of butter refers to what is 
called the grain and depends upon the condition of the 
butter-granules. In its first formation in churning, 
butter appears in very small, irregular grains or gran- 
ules. These grains retain their individuality in large 
measure throughout the rest of the process of butter- 
making and even in the finished product. The more 
distinct the individuality of the granules can be kept 
in making the butter into a solid mass, the better is 
the texture. 

Testing texture. — The granular texture of butter 
is seen when a plug or chunk of butter is broken into 
parts transversely, giving somewhat the fractured ap- 
pearance seen in broken steel and free from a smooth, 
greasy appearance. Another method of testing tex- 



154 MODERN METHODS OF TESTING MILK 

ture is to pass a knife-blade or butter-trier through 
the butter; when it is withdrawn, the trier is clean 
•and free from any greasy appearance, if the texture 
is good. 

Terms describing texture. — The terms used to de- 
scribe texture are (i) perfect, (2) poor grain, and 
(3) salvy. 

( 1 ) Perfect texture in butter is shown by the gran- 
ular formation, as described above. 

(2) Poor grain texture in butter is shown by less 
marked grain and a more or less smooth, greasy ap- 
pearance on the broken surfaces. 

(3) Salvy texture applies to butter in which the 
grain is more or less destroyed and the smooth, greasy 
appearance of the broken surface is very marked. 

Defective texture in butter is caused by allowing 
the butter-granules in the churn to become too large 
and by working too much or at too high a tempera- 
ture. The granular texture of butter is completely de- 
stroyed by warming butter to near its melting point. 

Body. — By this term is meant the quality of consis- 
tency, firmness or hardness, as shown by not melting 
or softening too easily. 

Testing body. — The body of a sample of butter can 
be ascertained by pressing a portion of the plug be- 
tween the thumb and fingers, and also by pressing be- 
tween the tongue and roof of the mouth. 

Terms describing body. — The terms used to de- 
scribe the body of butter are : ( i ) perfect, firm or 
solid, (2) hard or tallowy, (3) weak-bodied, (4) 
sticky. 



COMMERCIAL TESTING OF BUTTER AND CHEESE I55 

(i) Perfect body in butter is shown by firmness or 
solidity under proper conditions of temperature. When 
pressed between the fingers or on the tongue it shows 
a certain amount of resistance. 

(2) Hard or tallowy body is shown by excessive so- 
hdity, being characteristic of butter made from cows 
far along in lactation, or in the case of cows heavily 
fed on cotton-seed meal. 

(3) Weak-bodied butter is lacking in firmness, more 
or less soft, melting more easily on warming than a 
perfect-bodie4 butter. Weak-bodied butters are usu- 
ally salvy in texture and high in moisture. Certain 
feeds, such as gluten meal, tend to increase the soft- 
ness of butter. 

(4) Sticky body in butter is shown by extreme soft- 
ness amounting to stickiness. 

Moisture. — The water in butter should be so thor- 
oughly incorporated with the fat that it does not appear 
in the form of free beads of water visible to the eye. 
Water should not run off the trier when a sample is 
drawn. The water should also be clear and trans- 
parent. 

Testing moisture. — The sample of butter is exam- 
ined for the appearance of moisture or brine in respect 
to the completeness of its incorporation and its clear- 
ness. 

Terms describing moisture. — The following terms 
are used to describe the condition of moisture in but- 
ter: (i) Perfect, (2) excessive, (3) milky or turbid. 

(i) Perfect moisture in butter is shown by the ab- 
sence of any visible moisture in the form of drops. 

(2) Excessive moisture is shown by the presence of 



156 MODERN METHODS OF TESTING MILK 

water easily apparent to the eye. Butter may some- 
times contain so much water as to be called "mushy/' 

(3) Milky or turbid moisture or brine appears more 
or less milky, being due to the presence of too much 
buttermilk. 

Relation of texture, body and moisture. — Considera- 
ble confusion prevails in the use of the terms texture, 
body and moisture. Some use the term texture to in- 
clude also body and moisture; others use the term 
body to include texture, while others use the expres- 
sion "body and grain" to cover all three qualities. Tex- 
ture and body and moisture may be influenced by the 
same conditions and may be, to some extent, interde- 
pendent, but in reality they are distinct properties and, 
if they were treated as such, needless confusion would 
be avoided. 

Color. — The color of butter varies in different mar- 
kets according to requirements, but most of the but- 
ter made in the United States has, as its standard, an 
even, bright, straw-yellow. Most butter in commerce 
is colored artificially, so as to maintain a uniform ap- 
pearance at all seasons of the year. Somewhat dif- 
ferent shades of color are demanded by different mar- 
kets. 

Testing color. — The quality of color is tested 
simply by inspection with the eye. The thumb-nail is 
run along the surface of the plug near the edge of the 
trier, and the fresh surface thus made is examined. 
The examiner carries in his mind the shade of what 
he regards as an ideal color and judges the sample 
under examination by its comparison with his ideal. 
It would lead to easier methods of comparison and 



COMMERCIAL TESTING OF BUTTER AND CHEESE 1 57 

more uniform results if there could be agreed upon 
a certain shade of color which should serve as a na- 
tional standard as far as possible. Such a color stand- 
ard could be furnished butter-makers and examiners 
of butter. Along with such a standard color, there 
could be prepared a scale of shades which could serve 
as a basis for scoring color. 

Terms describing color. — The terms used in de- 
scribing the color of butter are: (i) perfect, (2) light, 
(3) high, (4) reddish, (5) mottled, and (6) white- 
specked. 

(i) Perfect color in butter is a straw-yellow, bright, 
and uniform throughout the mass. A plug of butter 
held between the light and the eye should be evenly 
translucent and not opaque or cloudy. 

(2) Light color is shown by insufficient color, the 
yellow being too pale. 

(3) High color is deeper yellow than called for by 
perfect color. 

(4) Reddish color is self-explanatory and is due to 
excessive use of coloring material. 

(5) Mottled color in butter is shown by the appear- 
ance of light-colored portions, which may be in spots 
or streaks or waves. The term zvavy is often used to 
indicate a variation of color that is just perceptible. 
They are not seen as readily on a sample plug drawn 
by a trier as they fcan be by cutting a lump of butter 
across so as to show a smooth, broad surface. Slight 
mottling is apt to escape observation when the exam- 
ination is made only of a plug. Mottling is due to 
the action of salt upon buttermilk retained in the but- 
ter. The light portions owe their color to the pres- 



158 MODERN METHODS OF TESTING MILK 

ence of the casein lactate of buttermilk. Removal of 
buttermilk from the butter-granules prevents mottling. 
(Bulletin No. 263, N. Y. Agr. Exp. Sta. 1905). 

(6) White-specked color in butter appears in white 
specks of varying size, but usually small. They are 
due to particles of coagulated casein lactate produced 
in cream by over-ripening, and also to dried cream 
particles, caused by lack of stirring during the process 
of ripening. 

Salt. — The amount of salt in butter varies with dif- 
ferent markets; but, whatever the amount used, it 
should be completely dissolved and evenly distributed 
through the mass of butter. 

Testing butter for salt. — The quality of butter as 
affected by salt is examined by tasting, sight and feel- 
ing. Undissolved particles of salt, when they can not 
be felt on the tongue or seen, can be detected by rub- 
bing some of the butter between the fingers. 

Terms describing salt. — The terms used in de- 
scribing the quality of butter in relation to salt are the 
following: (i) Perfect, (2) too salty, (3) flat, (4) 
gritty, (5) uneven. 

(i) Perfect quality in respect to salt in butter is 
shown as follows : The salt must be in the proportion 
demanded by the market; it must be entirely dissolved 
and evenly distributed. 

(2) Too salty butter contains more salt than the 
market demands. 

(3) Flat butter is lacking in salt for the market re- 
quirements. 

(4) Gritty butter contains undissolved salt. 



COMMERCIAL TESTING OF BUTTER AND CHEESE 1 59 

(5) Uneven salt in butter is lack of uniformity, some 
portions of butter being more salty than others. 

Appearance. — Under this head are included the 
manner of packing, the attractive appearance of the 
package, cleanliness, etc. 

Testing appearance. — When the cover of the pack- 
age is removed for sampling the butter, the appearance 
of the surface of the butter is noticed. The outside of 
the package is also examined. The two general quali- 
ties that must be kept in mind in this connection are 
cleanliness and neatness. 

Terms describing appearance. — The quality of ap- 
pearance of butter may be considered under two heads, 
(i) finish and (2) package. 

(i) Finish in appearance, in connection with exam- 
ining butter, refers to the manner of packing. The 
finish is perfect when the package is lined with paraf- 
fin or with a good quality of parchment paper, neatly 
placed, and the package well filled, the surface being 
even and bright. The package should be just evenly 
full. The top should be neatly covered with cheese- 
cloth saturated w^th brine. 

(2) Package. — The package is regarded as perfect 
when of good material, well-made, clean, and neat in 
appearance. In the same lot of butter the packages 
should all be alike in size and shape. 

SCORING BUTTER 

The different qualities indicated above are used in 
a specific manner for judging and fixing the com- 
mercial value of butter. 



l60 MODERN METHODS OF TESTING MILK 

Scale of points. — To each quality is assigned a defi- 
nite numerical value and these numbers are called a 
scale of points. The following scale of points is in 
common use in many markets of this country, the num- 
bers indicating perfect quality in each case, and the 
totals aggregating loo: 

Flavor, 45 points. Color, 15 points. 

Texture, (10) ) Salt, 10 points. 

Body, (10) [-25 points. Appearance, 5 points. 

Moisture, (5) ) Total, 100 points. 

Method of scoring. — In scoring a sample of but- 
ter, an examination is made with reference to each of 
the qualities mentioned. In those qualities in which it 
is perfect, it is given the values or points assigned 
above. If the butter is defective in any quality, that is, 
short of perfect, then a smaller value is given than the 
one indicated above in the scale of points ; the more de- 
fective the butter is in any quality, the lower is the 
value or number of points given it. When all the 
qualities have been scored, the numbers of points as- 
signed to them are added and the total is the score of 
the butter under examination. 

It can readily be seen that judgment, trained by ex- 
perience, is required to assign to each quality its proper 
number of points. The sense of smell and of taste 
must be highly developed by training in the field of 
experience. The eye and touch must also be trained 
by special experience. 

Score-cards. — For convenience, score-cards are used 
in keeping records of the results of scoring where many 
samples are examined. The following form illustrates 
a commercial score-card : 



COMMERCIAL TESTING OF BUTTER AND CHEESE l6l 



NAME OR NUMBER IDENTIFYING SAMPLE, 
DATE JUDGE 



QUALITY 


SCORE-POINTS 


Sample 


Sample 
2 


Sample 
3 


Sample 
4 




45 
10 
10 

5 
15 
10 

5 


45 

8 

,0 

13 
10 
4 


40 

10 
8 
3 
14 
10 
5 


36 

8 
8 
4 
13 
10 
4 


32 


Texture 




Body 


7 




4 


Color . . 


13 


Salt 


8 


Appearance 


5 




95 


90 


83 


75 



These scores, under the system of grading described 
below, would be graded as follows: Sample i, "ex- 
tras ;" sample 2, "firsts ;" sample 3, "seconds ;" and 
sample 4, "thirds." 

In commerical scoring, reasons for the number of 
points given are not stated ; but in dairy schools and 
competitive public exhibitions, where educational pur- 
poses are in view, the reason for each score should be 
given. The following form of score-card for such 
purposes is a suggestion, which may be modified to 
suit any special conditions : 

Butter-Scoring — Numerical and Descriptive Card 

Date Judge 

Name or number identifying butter 



l62 



MODERN METHODS OF TESTING MILK 



NUMERICAL SCORE. 

Perfection— Flavor, Texture, Body, Moisture, Color, Salt, Appearance 
(45) (10) (10) (5) (15) (10) (5) 

Score given — — — — — — — 

DESCRIPTIVE SCORE (check defects below). 



Flavor 


Texture 


Body 


Moisture 


Color 


Salt 


Appear- 
ance 


Perfect Quick 


Perfect 


Perfect 


Perfect 


Perfect 


Perfect 


Finish 


Clean I^ight 

Buttermilk 

Rancid 

Tallovpy 

Cowy 


Pooi- 
grain 

Salvy 


Firm 

Hard 

Weak- 
bodied 


Exces- 
sive 

Milky 


I,ight 
High 
Reddish 


Too salty 

Flat 

Gritty 


Package 


Fishy Tainted 




Sticky 




Mottled 


Uneven 




Stable Weedy 
Cheesy 








Wavy 
Specks 







CLASSES AND GRADES OF BUTTER 

The following system for classifying and grading 
butter is taken from the regulations of the New York 
Mercantile Exchange: 
Classification :— 

1. Creamery Butter includes butter made in a cream- 
ery from cream obtained by the separator system, or 
from gathered cream. 

2. Imitation Creamery Butter includes butter 
churned by the dairyman, collected in its unsalted, un- 
worked condition, and worked, salted and packed by 
the dealer or shipper. 

3. Dairy Butter includes such as is made, salted 
and packed by the dairyman and offered in its orig- 
inal package. 

4. Factory Butter is butter collected in rolls, lumps, 



COMMERCIAL TESTING OF BUTTER AND CHEESE 163 

or in whole packages, and reworked by the dealer or 
shipper. 

^.^ Renovated Butter is that made by taking pure 
butter and melting the same and rechurning with fresh 
milk, cream or skim-milk, or other equivalent pro- 
cess. 

6. Grease consists of all grades of butter below 
Fourths free from adulteration. 

7. Known Marks is a term used to include such 
butter as is known to the trade under some particular 
mark or designation and must grade as Extras, if 
creamery, and as Firsts, if reworked butter, in the 
season in which it is offered, unless otherwise speci- 
fied. 

Grades: — Grades of butter must conform to all 
the following requirements and are not determined by 
score alone. 

1. Extras must be of the highest grades of butter 
made in the season when offered under the different 
classifications ; 90 per cent, shall be up to the following 
standard and the balance must not grade below Firsts : 

(i)Flavor must be fine, sweet, clean and fresh, if 
of current make; and fine, swxet and clean, if held. 
(2) Body must be firm, smooth and uniform. (3) 
Color should be a light straw shade, even and uniform. 
(4) Salt should be medium. (5) Package should be 
good, uniform and clean. (6) Score must average 93 
points or higher. 

2. Firsts is a grade just below Extras and must 
be fine butter for the season when made and offered, 
under the different classifications, and up to the fol- 
lowing standard: 



164 MODERN METHODS OF TESTING MILK 

(i) Flavor must be good, sweet, clean and fresh, 
if of current make ; and good, sweet and clean, if held. 
(2) Body must be good and uniform. (3) Color must 
be reasonably uniform, neither too high nor too light. 

(4) Salt should be medium. (5) Packages should be 
good and uniform. (6) Score must average 87 points 
or higher. 

3. Seconds is a grade just below Firsts and must 
be good for the season when offered under the differ- 
ent classifications, and up to the following standard : 

(i) Flavor must be reasonably good and sweet. (2) 
Body, if creamery or dairy, must be solid-boring. If 
factory or renovated, must be 90 per cent, solid-bor- 
ing. (3) Color must be fairly uniform. (4) Salt may 
be high, medium or light. (5) Package should be 
good and uniform. (6) Score must average 80 points 
or higher. 

4. Thirds is a grade just below Seconds. 

( I ) Flavor must be reasonably good ; may be strong 
on top and sides. (2) Body should be fair-boring, if 
creamery or dairy, and at least 50 per cent, boring a 
full trier, if factory or renovated. (3) Color may be 
irregular. (4) Salt may be high, light or irregular. 

(5) Packages should be fairly uniform. (6) Score 
must average 75 points or higher. 

5. Fourths is a grade just below Thirds and may 
consist of promiscuous lots. 

( I ) Flavor may be off and strong on tops and sides. 
(2) Body is not required to draw a full trier. (3) 
Color may be irregular. (4) Salt may be high, light, 
or irregular. (5) Package may be of any kind men- 
tioned at time of sale. 



COMMERCIAL TESTING OF BUTTER AND CHEESE 165 

SAMPLING AND TESTING CHEESE 

Only the ordinary American cheese, usually made 
by the cheddar system, is here considered. For com- 
mercial testing, cheese is sampled by a cheese-trier 
in much the same manner as butter. The plug should 
always be drawn from the top and not from the side 
in order to avoid injuring the protective power of the 
bandage. The plug drawn is examined by smelling, 
feeling, appearance, etc., in reference to the various 
qualities mentioned below. 

TERMS USED IN DESCRIBING QUALITIES OF 
CHEESE 

The following qualities have been selected to serve 
as a basis in the commercial testing and scoring of 
cheese: (i) Flavor, (2) texture, (3) body, (4) color, 
(5) salt, and (6) appearance. 

Flavor. — By flavor is meant the quality that is per- 
ceptible to the smell and taste. The sense of smell is 
depended upon in testing flavor in cheese much 
more largely than is the sense of taste, because, in ex- 
amining a large number of samples of cheese in suc- 
cession, constant tasting soon dulls not only the sense 
of taste but also that of smell. Flavor in cheese is 
due to the formation of some unknown compound or 
compounds during the ripening process. 

Testing flavor in cheese. — The flavor is best ob- 
tained by direct smelling of the plug as soon as it is 
drawn and, in addition, by crushing and warming 
some of the cheese in the hand and then smelling. 

Terms used in describing cheese flavors. — From 
a great variety of names applied to various flavors 



1 66 MODERN METHODS OF TESTING MILK 

found in cheese, the following terms are selected for 
consideration: (i) Perfect, (2) high or quick, (3) 
clean, (4) low or flat, (5) strong, (6) too much acid, 
(7) too little acid, (8) sour, (9) sweet or fruity, (10) 
rancid, (11) tallowy, (12) tainted, (13) stable, (14) 
weedy, (15) bitter, (16) cowy. 

(i) Perfect flavor applies to cheese when it some- 
what resembles that of first-class butter with an added 
quality of its own that is characteristic but cannot be 
described further than to call it cheese-like. It is 
sometimes described as "nutty." This flavor should 
be marked, but not strong. It should be free from 
all other flavors, particularly the more or less offen- 
sive products of undesirable fermentations.. The taste 
should be mild and somewhat lasting, but should not 
be so sharp as to ''bite" the tongue. 

(2) High or quick flavor is a delicate flavor that dis- 
appears quickly. 

(3) Clean flavor is free from every trace of unpleas- 
ant aroma or taste. 

(4) Low or flat flavor applies to slight traces, or 
absence, of flavor; it is insipid. 

(5) Strong flavor is a good flavor very pronounced 
but free from everything offensive; it is a good flavor 
strongly developed. 

(6) Too much acid applies to flavor that smells 
somewhat sour but does not taste sour. 

(7) Too little acid applies to a mild flavor, lacking 
in character. 

(8) Sour flavor is characterized by a sour taste 
when the cheese is fresh, owing to the presence of too 
much whey. 



COMMERCIAL TESTING OF BUTTER AND CHEESE 167 

(9) Sweet or fruity flavor is suggestive of artificial 
pineapple odor and is somewhat "sickish." 

(10) Rancid flavor is that of butyric acid, more com- 
mon in old cheese than in young. When very strong, 
it affects a delicate throat with a slight sensation of 
choking or strangling. 

(11) Tallozvy flavor is like that of tallow. 

(12) Tainted flavor includes a variety of odors, 
mildly to strongly offensive. 

(13) Stable flavor suggests the smell of cow- ma- 
nure. 

(14) Weedy flavor applies to such abnormal flavors 
as come from onions, leeks, cabbages, ragweed, etc. 

(15) Bitter flavor is self-descriptive. It is often due 
to certain fermentations that develop when a cheese 
is undersalted. 

(16) Coivy flavor is suggestive of the breath of a 
cow and may develop in cheese from some form of 
fermentation. 

Texture. — Texture, as applied to cheese, refers 
chiefly to compactness or appearance of solidity, and 
has a meaning quite different from what it has when 
used with reference to butter. It is quite common to 
regard the *'body" as a part of the texture, but the 
two qualities are clearly distinct. 

Testing texture in cheese. — The texture of cheese 
is tested by an examination of the plug with reference 
to the presence of holes. The plug is broken in two 
and the broken ends examined for the characteristic 
flinty appearance. 

Terms describing texture. — The following terms 
are among those most commonly used in describing 



l68 MODERN METHODS OF TESTING MILK 

texture: (i) Perfect, (2) close, (3) loose, (4) me- 
chanical holes, (5) gas or pin-holes, (6) Swiss holes. 

( 1 ) Perfect texture in cheese is shown when a plug 
or a cut surface of the inside of the cheese presents 
to the eye a solid, compact, continuous appearance, 
free from breaks, holes and chunks. When a plug 
is broken in two, it should show a flaky appearance, 
termed a "flinty" break, resembling the surface of 
broken flint or steel. 

(2) Close texture describes the appearance of a 
cut surface of cheese when free from all kinds of 
holes. 

(3) Loose or porous texture is indicated by lack of 
solid compactness, being more or less full of holes, 
which vary from a few to enough to make a spongy 
appearance. 

(4) Mechanical holes in cheese are irregular, open 
spaces, caused by the incomplete cementing of the 
pieces of curd in the press. 

(5) Gas-holes or pin-holes are small holes, produced 
by gaseous products of fermentation. 

(6) Szviss holes are fairly large, round holes, such 
as are present in Emmenthaler cheese. 

Body. — This term, used in connection with cheese, 
refers to the consistency, firmness or substance of 
cheese. It is largely influenced by the amount of 
fat and moisture in cheese. 

Testing body. — This quality is found by pressing a 
piece of cheese between the thumb and fingers. 

Terms describing body. — The following terms are 
among those used in describing the body of cheese: 
(i) Perfect, (2) solid or firm, (3) smooth, (4) silky, 
(5) waxy, (6) pasty or salvy, (7) stiff, corky, or 



COMMERCIAL TESTING OF BUTTER AND CHEESE IDQ 

curdy, (8) weak-bodied, (9) mealy, (10) gritty, (11) 
watery, (12) oyer-dry. 

( 1 ) Perfect body in cheese is indicated when it feels 
solid, firm and smooth in its consistency or substance. 
It does not crumble under pressure. A plug drawn 
from a cheese of perfect body should be smooth in ap- 
pearance and not "fuzzy." 

(2) Solid or Urm body is indicated when cheese of- 
fers a certain amount of resistance under pressure, 
somewhat like that shown by a piece of fat pork or 
cold butter. The term meaty is also used. 

(3) vSmoo/Zi -bodied cheese, when pressed between 
the thumb and fingers, feels smooth and velvet-like, as 
distinct from harsh, gritty or mealy. 

(4) Silky-hodi&d cheese is smooth in feeling but not 
over-solid in consistency. 

(5) Waxy-ho^\td cheese is much the same as silky 
but possessing more firmness or solidity. 

(6) Pasty or salvy cheese is very soft, usually from 
an excess of moisture. When pressed, it sticks to the 
fingers. 

(7) Stiif, corky or curdy cheese is hard, tough, over- 
firm ; it does not crush down readily when pressed in 
the hand. 

(8) f^^a^-bodied cheese is very soft, lacking in 
firmness but not necessarily sticky like pasty cheese. 

(9) Mealy cheese breaks down in fine crumbs when 
pressed. 

(10) GnV/y-bodied cheese feels harsh and gritty 
under pressure. 

(11) ^fl^^ry-bodied cheese is excessively soft, pasty 
and sticky. 



170 MODERN METHODS OF TESTING MILK 

(12) In an over-dry cheese the body is very hard 
or mealy. 

Color. — The color of cheese varies considerably, 
whether artificially colored or not. There appears to 
be an increasing demand for uncolored cheese. The 
coloring varies from a pale yellow to a reddish yel- 
low, according to the demands of special markets. 

Testing color. — The color is tested by inspection 
with the eye, the examiner noticing particularly unev- 
enness and any extreme condition of color. 

Terms describing color. — Color in cheese is de- 
scribed by the following terms: (i) Perfect, (2) 
straight, (3) translucent, (4) white specks, (5) streak- 
ed, (6) wavy, (7) mottled, (8) acid-cut, (9) high, 
(10) light, (il) uncolored. 

(i) Perfect color in cheese is indicated by evenness 
of color throughout the mass. A plug held between 
the eye and light should appear somewhat translucent. 

(2) Straight color is an even, uniform color through 
the whole cheese. 

(3) Translucent applies to color in cheese which 
appears slightly translucent when the plug is held be- 
tween the eye and the light. 

(4) White specks is a term that describes itself. 
Such specks in cheese are a defect. They may appear 
in cheese cured at low temperature. 

(5) Streaked color indicates that there are light- 
colored portions in the form of streaks. 

{6)Wavy color applies to lighter portions appear- 
ing in the form of waves. 

(7) Mottled color shows in cheese in lighter-colored 
spots of fairly large size^, more or less irregular. 



COMMERCIAL TESTING OF BUTTER AND CHEESE I7I 

(8) Acid-cut color is shown in cheese when consid- 
erable portions of the cheese have been made lighter 
in color by the presence of too much acid (whey). 

(9) High color is indicated by a reddish color, 
caused by using too much coloring matter. How- 
ever, the question of color is a relative one, because 
the demand in different markets varies from uncolored 
to extremely high color. 

(10) Light color is the term usually used in describ- 
ing cheese that has been made uniformly dead white 
by the action of too much acid (whey). 

(11) Uncolored cheddar cheese is not white but of 
a light amber shade. 

Salt. — The amount of salt in cheese varies somewhat 
with different markets. There is seldom experienced 
difficulty of uneven salting in cheese, because the salt 
slowly permeates the cheese in the ripening process. 
Little variations usually occur in different parts of 
the same cheese, but are so slight as to be incapable of 
being noticed by ordinary methods of examination. 

Testing cheese for salt. — The quality of cheese as 
influenced by the salt is found simply by tasting. 

Terms used in describing salt. — In describing the 
relation of salt to cheese, the following terms are used : 
(i) Perfect, (2) too much, (3) too Httle. 

(i) Perfect applies to salt in cheese when just 
enough has been used to impart a sufficient taste of 
salt. 

(2) Too much salt is indicated by salty taste. Too 
much salt in cheese causes a dry, mealy texture, over- 
firm body and imperfect flavor. 

(3) Too little salt is shown by insipidity of taste. 



172 MODERN METHODS OF TESTING MILK 

It is usually accompanied by bitter flavor and porous 
texture. 

Appearance. — This term refers to the general ap- 
pearance of the cheese to the eye in respect to uni- 
formity, neatness and cleanliness. It may also include 
the boxing. One system, as in the case of butter, de- 
scribes under "finish" the appearance of the cheese, and 
under "packages" the boxing; and we will follow this 
method here. 

Testing appearance. — When the cover of the box 
is removed for sampling, in the case of boxed cheese, 
the appearance of the cheese is noticed and the box 
itself is examined. Cleanliness and neatness are 
the points to observe in judging appearance. 

Terms describing appearance. — The general terms 
used in describing appearance are (i) finish and (2) 
package. 

(i) Finish in appearance, in order to be perfect, 
must meet the following requirements : The rind must 
be smooth, even in color, free from cracks and fairly 
hard. The bandage must be without wrinkles and 
must be neatly rounded over the edges about an inch 
and a half on each end of the cheese. The sides of 
the cheese should be straight and of uniform height 
all around. 

The faults of appearance in finish are as follows, the 
terms being self-descriptive: (i) Cracks, (2) Hght 
spots, (3) roughness in rind, (4) uneven edges, (5) 
wrinkles in bandage, (6) lack of uniformity in ends 
and in height, (7) bulging out at sides or ends. 

(2) Package. — The packages or boxes are regarded 
as perfect when of good material, well made, strong, 



COMMERCIAL TESTING OF BUTTER AND CHEESE I73 

clean, close-fitting, uniform in size and in undamaged 
condition. 

SCORING CHEESE 

The qualities described in the preceding pages are 
used for judging and fixing the commercial value of 
cheese. 

Scale of points. — The following scale of points is 
in use in many places, the numbers indicating perfect 
quality in each case and the totals aggregating lOo: 

Flavor, 50 Body, 15 Salt, 5 

Texture, 15 Color, 10 Appearance, 5 

In the practice of many markets, salt is omitted and 
appearance is given lo points. 

Method of scoring. — The general procedure is es- 
sentially the same as that already described in connec- 
tion with butter (p. i6o). 

Method of grading cheese. — The same general prin- 
ciples apply as in grading butter (p. 163). One class- 
ification is into (i) "fancy," (2) ''firsts," and (3) 
"seconds." In the Canadian market, there are first, 
second and third grades. 

Score-cards for cheese can be prepared in a manner 
similar to those previously suggested for butter (p. 162) . 

As in the case of butter, the testing, scoring and 
grading of cheese demand good judgment trained by 
experience. The sense of smell and touch must be 
well developed. 

No formal classification or grading of cheese is 
made by the New York Mercantile Exchange, as is 
done in the case of butter. 



CHAPTER XIV 

Methods of Commercial Testing and Scoring 
of Milk and Cream 

The only basis commonly used in judging the qual- 
ity of market milk is the percentage of fat and solids. 
The chief effort of many sellers of milk is confined to 
making sure that the milk conforms in fat and solids 
to the requirements of the legal standard. In New 
York City the temperature of the milk when it reaches 
the city is made an important point of quality by the 
milk-inspectors. In some special cases, as yet too few, 
cleanliness is also made a point of commercial quality, 
as in the case of condenseries and as shown by the 
standing of certified milk, (milk produced under con- 
ditions, and reaching certain standards, that are ap- 
proved by a city health department). In most cream- 
eries and many cheese-factories, the percentage of fat 
in milk is made the chief or only basis of valuation. 

The absence of a definite basis for judging market 
milk commercially is due to several reasons. Consu- 
mers usually take what they get without much ques- 
tion, protected only by the legal standard. In the 
next place, the opportunity for examination is lim- 
ited, owing to the perishable nature of milk. Again, 
it is not possible to examine milk wholly by the senses, 
as is done in the case of butter and cheese ; more time 
must be consumed and different means employed, in 

174 



COMMERCIAL TESTING OF MILK AND CREAM I75 

order to reach a satisfactory judgment of the qual- 
ity of milk. 

In the past few years, attention has been concen- 
trating upon the character of market milk, and there 
has been a gradually growing sentiment that some 
method of testing the commercial value of milk and 
cream, similar to that used in judging butter and 
cheese, ought to be developed. It is the purpose of 
the writer to propose and discuss a method for judg- 
ing and scoring milk and cream in the hope that it 
may serve as a beginning, however tentative, which 
will lead to the development of a practical and useful 
system. 

Three factors determine most largely the commercial 
value of market milk: (i) The composition of the 
milk, (2) the length of time it will remain sweet and 
palatable, (3) the flavor, or taste and odor, of the 
milk, and, we may add, though of less importance, (4) 
the color of the milk. 

Composition of milk in relation to commercial 
testing and scoring. — The composition of milk, other 
things being equal, determines its value as food, its 
nutritive value ; and this should constitute a large fac- 
tor in judging the value of market milk. The two 
factors which can be used as a means of determining 
the composition of market milk are fat and solids-not- 
fat. These are easily determined (p. 53 and p. 129). 

What amount of fat and solids-not-fat shall count 
as perfect in market milk? The figures used should 
represent as nearly as possible normal milk of average 
composition, and, according to results of the writer's 
study of many thousand analyses of American milks, 



176 MODERN METHODS OF TESTING MILK 

the correct amounts would be about 4 per cent, of fat 
and 9 per cent, of solids-not-fat. This basis is prefer- 
able to the use of a legal standard, because legal stand- 
ards prescribe the lowest permissible amounts of fat 
and solids-not-fat, while milk that can be regarded as 
deserving a perfect score in composition should surely 
be above the low amounts allowed by legal standards. 
Some might claim that a composition of 4.5 or 5 per 
cent, of fat content and 9.2 or 9.3 per cent, of solids- 
not-fat should be used as representing milk of perfect 
composition. The medium composition between this 
high extreme and the low extreme of a legal standard 
should appeal to one on careful thought as the wisest 
basis for scoring the composition of milk. 

Using 4 per cent, of fat and 9 per cent, of solids- 
not-fat as indicating the basis of a perfect score in 
composition in market milk, the next question that 
arises is as to how many points out of 100 shall be al- 
lowed for a perfect score in composition. In the writ- 
er's judgment, not less than 45 points should be al- 
lowed for perfect composition. Then, for each one- 
tenth of one per cent, of fat below 4 and of solids-not- 
fat below 9, there should be a reduction of one point. 
Thus, milk testing 3.5 per cent, of fat and 8.8 per cent, 
of solids-not-fat would be scored 38 points on com- 
position. 

Keeping power of milk in relation to commercial 
testing and scoring. — The length of time milk remains 
sweet and palatable for table use is commonly indi- 
cated as its keeping power or quality. This is an im- 
portant factor in estimating the commercial value of 
market milk, since sour or unpalatable milk, or milk 



COMMERCIAL TESTING OF MILK AND CREAM I77 

containing any undesirable form of fermentation, is 
comparatively valueless for direct use, however rich 
it may be in fat and solids-not-fat. The keeping power 
of milk depends upon (i) the number and kind of 
bacteria present and (2) the temperature of the milk. 
Knowledge of the keeping quality of milk can be 
gained (i) by knowing the number of bacteria pres- 
ent, (2) by determining the acidity, (3) by estimating 
the amount of dirt suspended in milk, and (4) by mak- 
ing fermentation tests of the milk. Since considerable 
time and expert skill are required to determine the 
number of bacteria in milk, the determination of this 
factor may commonly prove impracticable in the case 
of ordinary market milk; but the acidity of the milk, 
the fermentation test and the amount of dirt in sus- 
pension will afford a satisfactory basis for judging 
the keeping power of milk. The acidity may be 
quickly learned by the methods given in Chap. VII. 
The fermentation test can be made in the manner de- 
scribed on p. 106. The amount of dirt in milk may be 
easily estimated as described on p. 109. 

How many points shall be allowed for the keeping 
quality of milk? Owing to the importance of this 
quality, it would seem as if it should be given at least 
35 points for perfection, which should mean entire 
freedom from dirt in suspension, a total acidity not 
exceeding. 1 8 per cent., and no development of gaseous 
or offensive fermentation. Deduction of points for 
dirt would have to depend to some extent on the judg- 
ment. For acidity, there should be deducted one point 
for each .01 per cent, of acidity above .18. In case 
the number of bacteria is determined, the milk should 



1/8 MODERN METHODS OF TESTING MILK 

score as perfect in keeping quality, when the number 
of bacteria is not over 100,000 per cubic centimeter, 
and one point should be deducted for each additional 
100,000. Experience and judgment in the interpreta- 
tion of the results of the fermentation test will be 
developed by practice. The appearance of porous curd 
and the development of abnormal odors should reduce 
the score. 

Flavor in milk in relation to commercial judging. 
— In ordinary market milk, properly handled, there 
should be no marked odor and nothing in the least 
offensive. The taste should be slightly saline and 
rich but without other marked features. There should 
not be any unpalatable after-taste. The abnormal odors 
and tastes that are noticeable in market milk, other- 
wise good, usually come from two sources : ( i ) From 
things eaten by the cow, as leeks, onions, rag-weed, 
cabbage, etc. (2) From the direct absorption of strong- 
smelling substances present in the air surrounding 
the milk ; among such odors thus absorbed by milk are 
those of manure, ensilage, turnips, etc. The presence 
of such abnormal odors in milk, if not readily percep- 
tible, can be more readily perceived by placing some 
of the milk in a tightly closed, perfectly clean fruit- 
jar or bottle and warming to 100° F. for a few min- 
utes. On opening the jar or bottle after such heating, 
any abnormal odor should be easily noticed. 

Milk is of perfect flavor when it is free from any 
abnormal odor or taste, but not insipid. The number 
of points to be allowed for flavor in market milk 
should be about 15, since flavor does not hold the 
same important relation to market milk that it does 
to cheese and butter. 



COMMERCIAL TESTING OF MILK AND CREAM I79 

Color of milk in relation to commercial judging. — 
Market milk should be of a slightly yellowish color, 
strikingly different from the white or bluish color of 
skimmed or watered milk but not as deep as the 
color of cream. Milk may be artifically colored, but 
is then very apt to be too high in color or not of the 
right shade of color. Color in milk is, perhops, of 
comparatively little importance but it has some signifi- 
cance to the eye of an expert. For perfect color 5 
points are assigned, with reduction for too little or 
too much color or for color otherwise abnormal. 

We are now in a position to summarize our discus- 
sion and present, in a more comprehensive manner, 
the method proposed for the commercial testing and 
scoring of market milk. 

TERMS USED IN DESCRIBING QUALITIES OF 
MARKET MILK 

The qualities selected to serve as a basis in the com- 
mercial testing and scoring of market milk are the fol- 
lowing: (i) Composition, (2) keeping power, (3) 
flavor and (4) color. 

Composition is used here to mean the amount of 
fat and of solids-not-fat. 

Testing composition. — The percentages of fat and 
of solids-not-fat are obtained in the manner described 
on p. 53 and p. 129. 

Terms describing composition. — Only two terms 
are here used in describing the composition of milk, 
(i) perfect and (2) defective. 

(i) Perfect, as applied to testing and scoring milk, 



l80 MODERN METHODS OF TESTING MILK 

means milk containing not less than 4 per cent, of fat 
and not less than 9 per cent, of solids-not-fat. 

(2) Defective applies to milk containing less fat 
or solids-not-fat than required for milk of "perfect" 
composition. 

Keeping power is an expression used to indicate in 
a general way the length of time milk remains sweet 
and palatable for table use. 

Testing keeping power. — The keeping power of 
milk is tested by making determinations of (i) the 
acidity (pp. 88-100) (2) the dirt in suspension, (p. 
109) (3) the fermentation test (p. 106) and, when 
practicable, (4) the number of bacteria. 

Terms describing keeping power. — The terms used 
in describing the keeping power of milk are (i) per- 
fect, (2) acidity, (3) dirt in suspension, (4) undesira- 
ble fermentations, and (5) number of bacteria per 
cubic centimeter. 

(i) Perfect. — Milk is called perfect in respect to 
its keeping power (a) when its acidity is not above .18 
per cent, (b) when it contains no dirt in suspension, 
(c) when the fermentation test reveals nothing ab- 
normal, and (d) when the number of bacteria does 
not exceed 100,000 per cubic centimeter. 

(2) Acidity is used to mean the amount of apparent 
total acid calculated as lactic, as shown by the amount 
of alkali neutralized. 

(3) Dirt in suspension is a self-explanatory expres- 
sion. 

(4) Undesirable fermentations refer to the results 
of the fermentation test. They may reveal themselves 
in causing porous, spongy curd and in producing of- 
fensive odors. 



COMMERCIAL TESTING OF MILK AND CREAM l8l 

(5) Number of bacteria per cubic centimeter is a 
self-descriptive term. 

Flavor, applied to milk, is used to mean the odor 
and taste. 

Testing flavor. — This is done by tasting and smell- 
ing the milk. The presence of abnormal odors can 
be more readily perceived by heating the milk for a 
few minutes to 100° F. in a closed bottle or jar and 
then smelling at once on opening the vessel. 

Terms describing flavor. — The following terms may 
be used in describing the flavor of market milk : ( i ) 
Perfect, (2) stable or cow manure, (3) leeks or on- 
ions, (4) ensilage, (5) cabbage, turnips, etc., (6) bit- 
ter, (7) tainted. 

(i) Perfect flavor in market milk is indicated by 
freedom from all traces of abnormal odor and taste. 
There should be no marked odor and no trace of any 
offensive smell. The taste should be palatable, slightly 
saline and rich, without any unpalatable after-taste. 
It should not be flat and insipid. 

The other terms are mostly self-descriptive. The 
term tainted is used to cover miscellaneous offensive 
flavors not included under the other terms. 

Color in relation to the testing and scoring of mar- 
ket milk explains itself. 

Testing color. — The color is examined by direct in- 
spection in a clear light. 

Terms describing color. — In describing the color 
of market milk, the following terms are used : ( i ) Per- 
fect, (2) white, (3) bluish, (4) high color, (5) red- 
dish. 

(i) Perfect as applied to color in milk indicates a 



l82 MODERN METHODS OF TESTING MILK 

yellowish color, not too pronounced. The other terms 
explain themselves. 

High color may be caused by artificial coloring, and 
reddish color is usually so caused. 

SCORING MILK 

The qualities described above are intended for use 
in the commercial judging and scoring of market milk. 

Scale of points. — The following scale of points is 
suggested for the reasons previously given, the num- 
ber indicating perfect quality in each case and the 
totals aggregating lOo: 

Composition, 45 Color, 5 

Keeping power, 35 Flavor, 15 

Method of scoring. — The milk is examined in the 
manner previously described and defects are indicated 
by deductions from the perfect score in the following 
manner : 

(i) Coniposition. — The perfect score of 45 points is 
reduced one point for each .1 per cent, below 4 per 
cent, of fat and 9 per cent, of solids-not-fat. 

(2) Keeping pouter. — The perfect score of 35 is to 
be reduced (a) one point for each .01 per cent, of acid- 
ity above 0.18, (b) a certain number of points, ac- 
cording to the judgment of the examiner, for dirt 
in suspension, (c) also for any abnormal results shown 
by the fermentation test, and (d) one point for each 
100,000 bacteria above 100,000 in one cubic centimeter 
of milk, when this determination is made. 

(3) Flavor. — The perfect score of 15 is reduced by 



COMMERCIAL TESTING OF MILK AND CREAM 183 

the presence of abnormal odors or tastes. The exam- 
iner must use his judgment as to the amount of re- 
duction. 

(4) Color. — The perfect score of 5 is reduced for 
too great variations from the normal color of milk. 

COMMERCIAL TESTING AND SCORING OF CER- 
TIFIED AND OF STANDARDIZED MILK 

Certified milk usually guarantees ( i ) the per c6nt. 
of fat, (2) the per cent, of total solids or solids-not-fat 
and (3) bacteria below a specified number. Standard- 
ised milk usually guarantees only the per cent, of fat. 

The examination and scoring of certified or of 
standardized milk are conducted in the same manner 
as in the case of market milk, except that the scoring 
is based upon the guarantees so far as these are given. 
The guaranteed per cent, of fat and of solids or solids- 
not-fat and the number of bacteria are to be taken as 
representing the perfect score in place of the figures 
given above for market milk, and deductions from the 
perfect score for defects are made on the basis of the 
guarantees. For example, if a certified milk is guar- 
anteed to contain 5 per cent, of fat, then, in order to 
be scored 45, the milk must contain 5 per cent, of fat 
and, in case of any shortage, a proportionate reduction 
should be made from the perfect score of 45. 

COMMERCIAL TESTING AND SCORING OF 
CREAM 

The manner of examining and scoring cream is 
essentially the same as in the case of milk. In com- 



184 MODERN METHODS OF TESTING MILK 

position cream is not examined or scored for solids, 
but only for fat. The per cent, of fat in cream calling 
for a score of 45 should be not less than 20 per cent., 
and there should be a reduction of one point for each 
one-half per cent, below 20. 



CHAPTER XV 



Arithmetic of Milk and Milk Products 

In connection with the testing of milk and milk 
products, especially in some of the practical applica- 
tions, various arithmetical calculations are often nec- 
essary. Special attention may need to be given to the 
methods employed in solving such problems as are 
presented, and a few pages are here devoted to the 
treatment of some of the more common problems in 
a systematic, comprehensive form, convenient for ready 
reference. In creameries, cheese-factories, etc., where 
much arithmetical work is involved in making divi- 
dends, saving of time is effected by using calculations 
or tables, which are published in book form. 

I. FINDING WEIGHT OF ANY CONSTITUENT 

Rule. — To find the weight of any constituent in milk 
or milk products, when the weight of the milk or its 
product and the per cent, of the constituent are known, 
multiply the zveight by the number indicating the per 
cent, of the constituent and divide the result by lOO. 
Example: How many pounds of fat in 675 pounds 
of milk testing 4.6 per cent, of fat? ^^^^^ = 3I-05j 
the number of pounds of fat. 



185 



ICX3 



l86 MODERN METHODS OF TESTING MILK 

EXAMPLES FOR PRACTICE 

(i) How many pounds of fat in 2,000 pounds of 
cheese containing 35 per cent, of fat? 

(2) How much water in 1,000 pounds of butter 
containing 14.5 per cent, of water? 

(3) How many grams of milk-sugar are there in 
500 grams of milk containing 5 per cent, of milk- 
sugar ? 

(4) How much fat is there in 1,200 pounds of 
cream testing 44 per cent, of fat? 

(5) How much fat is there in 5,000 pounds of skim- 
milk testing .15 per cent, of fat? 



2. FINDING PER CENT. OF ANY CONSTITUENT 

Rule. — To find the per cent, of any constituent in 
milk, etc., when the weight of the milk, etc., and the 
weight of the constituent are known, multiply the 
zveight of the constituent by 100 and divide the result 
by the weight of the milk, etc. Example: What is 
the per cent, of fat in 675 pounds of milk containing 
31.05 pounds of fat? ^^^^|^ = 4.6 per cent. 

EXAMPLES FOR PRACTICE 

(i) What is the per cent, of fat in 120 pounds of 
butter containing 96 pounds of fat? 

(2) What is the per cent, of water in 600 pounds 
of cheese containing 210 pounds of water? 



ARITHMETIC OF MILK AND MILK PRODUCTS 187 

3. FINDING PER CENT. OF SOLIDS IN MILK 

Rule. — To find the per cent, of solids in milk when 
the Quevenne lactometer reading and the per cent, 
of fat are known, divide the lactometer reading by 4, 
and to the result add the per cent, of fat multiplied by 
1.2. (See p. 129.) 

4. FINDING PER CENT. OF SOLIDS-NOT-FAT 
IN MILK 

Rule. — To find the per cent, of solids-not-fat in 
milk when the Quevenne lactometer reading and the 
per cent, of fat are known, divide the lactometer read- 
ing by 4, and to the result add the per cent, of fat 
multiplied by .2. (See p. 129.) 

EXAMPLES FOR PRACTICE UNDER RULES 
3 AND 4 

(i) What is the per cent, of solids in milk testing 
4 per cent, of fat and showing a lactometer reading 
of 32? 

(2) What is the per cent, of solids-not-fat in the 
same milk as in ( i ) ? 

(3) What is the per cent, (a) of solids and (b) of 
solids-not-fat in a milk testing 2.5 per cent, of fat 
and showing a lactometer reading of 27? 

(4) What is the per cent, (a) of solids and (b) of 
solids-not-fat in milk testing .2 per cent, of fat and 
showing a lactometer reading of 36? 



l8o MODERN METHODS OF TESTING MILK 

5. FINDING THE "OVERRUN" IN BUTTER- 
MAKING 

The weight of butter produced is greater than the 
amount of fat in the milk or cream from which the 
butter is obtained, because butter, in addition to its 
fat, contains water, salt and curd. Such excess is 
called the "overrun" and may be readily ascertained 
by finding the yield of butter for one pound of fat. 
While some milk-fat is lost in the skim-milk and but- 
termilk and in handling during butter-making, enough 
water, salt and curd are added to the fat to make up 
these losses and something more. The amount of but- 
ter yield for a pound of fat in milk or cream neces- 
sarily varies with the variation of losses of fat in skim- 
milk and in butter-making and the amount of water, 
salt, etc., retained in the butter. Hence the "overrun" 
varies. When the operations of skimming milk and 
butter-making are properly managed, one pound of 
fat in milk produces about 1.17 (about i 1-6) pounds 
of butter. Hence, the "overrun" is .17. or one-sixth, 
(17 per cent). The "overrun" in case of cream aver- 
ages about .03 higher than in case of milk, according 
to Hills. 

Rule. — To find the "overrun" when the weight 
of butter made from a given amount of milk or cream 
and the per cent, of fat in the milk or cream are known, 
Und the number of pounds of fat in the milk or cream 
by Rule i, and divide the weight of butter by the zueight 
of fat. From the result subtract i. Example: What 
is the "overrun" in case of milk testing 4 per cent, of 



ARITHMETIC OF MILK AND MILK PRODUCTS 189 

fat, when we make 135 pounds of butter from 3,000 
pounds of milk? Applying Rule i, ^"^^"^ =120, pounds 
of fat in milk; and 135^120=1.125 (1%) pounds. 
1. 125 — I =.125 (12.5 per cent.) or %. Therefore, the 
"overrun" is .125 or ^ pound, that is, for each pound 
of fat in milk there will be made i^ pounds of butter. 

6. FINDING THE YIELD OF BUTTER 

Rule. — To find the yield of butter when the per 
cent, of fat in milk and the weight of milk are known, 
find the number of pounds of fat in milk by Rule i 
and multiply this result by i.iy or i 1-6. Example: 
How much butter is made from 1,000 pounds of milk 
containing 4 per cent, of fat? Applying Rule i, 
1000x4 __ ^Q^ pounds of fat in milk; and 40x1.17= 
46.8, pounds of butter yield. 

In the case of cream apply the foregoing rule, ex- 
cept to multiply by 1.20 instead of 1.17. 

The application of this rule finds use in checking 
creamery work. If the yield, in case of milk, is not 
in proportion to an ''overrun" of 15 to 17 per cent, 
and in case of cream, 20 per cent., one should ascer- 
tain why and then correct such faults as aj-e found to 
exist in the form of losses of fat or retaining too little 
water. When the proportion of butter to fat greatly 
exceeds 1.17 in the case of milk, too much water is 
retained in the butter, or else the fat-test is improperly 
made or the results purposely read too low. 



190 MODERN METHODS OF TESTING MILK 

EXAMPLES FOR PRACTICE UNDER RULES 
5 AND 6 

(i) How much butter should be made from 5,000 
pounds of milk testing 5 per cent, of fat? 

(2) What is the "overrun" when 4,000 pounds of 
milk, testing 4 per cent, of fat, yield 180 pounds of 
butter? 

(3) A butter-maker has 10,000 pounds of milk, test- 
ing 4 per cent, of fat; in skimming this, he produces 
8,000 pounds of skim-milk, testing .15 per cent, of 
fat. After churning, he has 1,600 pounds of butter- 
milk testing .2 per cent, of fat. The loss of fat in 
handling the cream and making the butter amounts to 
4 pounds, (a) How much fat is left in the butter? 

(b) How many pounds of butter should be made? 

(c) What is the ''overrun" if he produces 450 pounds 
of butter? 

(4) How much butter should be made from 1,000 
pounds of cream testing 35 per cent, of fat? 

7. FINDING YIELD OF CHEESE FOR MILK-FAT 

Rule. — To find the yield of green cheese for a pound 
of fat in milk when the weight of the cheese made 
from a given amount of milk and the per cent, of fat 
in milk are known, find the number of pounds of fat 
in milk by Rule i, and divide the iveight of cheese by 
the weight of fat. Example: How much cheese is 
made for one pound of fat in milk, testing 4 per cent. 
of fat, when we make 63 pounds of cheese from 600 
pounds of milk? Applying Rule i, ^°° ^ ^ ,^ 24 
pounds of fat in milk; 63-^24=2.67 pounds of cheese 



ARITHMETIC OF MILK AND MILK PRODUCTS I9I 

made for one pound of fat in milk. In connection with 
cheese, this is the same kind of relation as the "over- 
run" in butter. In cheese-making a pound of fat 
in milk has added to it enough casein, water, salt, 
etc., to increase the weight from i of fat to 2."] (more 
or less) pounds of cheese. 

8. FINDING YIELD OF CHEESE FROM FAT IN 
MILK 

Rule. — To find the yield of green cheese from loo 
pounds of milk when the per cent, of fat in milk is 
known, multiply the per cent, of fat in milk by 2.7. Ex- 
ample: How much cheese should be made from 100 
pounds of milk testing 3.7 per cent, of fat? 2>'7^^'7^^ 
9.99 pounds. 

This rule applies only to normal milk containing 
3.6 to 3.8 per cent of fat. For milk containing fat 
above 3.8 per cent., the results are usually too high; 
and for milks containing less than 3.6 per cent, of 
fat, the results are usually too low. 

9. FINDING YIELD OF CHEESE FROM FAT AND 
CASEIN IN MILK 

Rule. — To find the yield of green cheese from 100 
pounds of milk when the per cent, of fat and of casein 
in milk is known, multiply the per cent, of casein by 
2.5 and to this result add the per cent, of fat multiplied 
by I.I. Example: How much cheese can be made 
from 100 pounds of milk containing 4 per cent, of 
fat and 2.6 per cent, of casein? (2.6x2.5) + (4xi.i) = 
10.90 pounds of green cheese. 



192 MODERN METHODS OF TESTING MILK 

10. FINDING PER CENT. OF CASEIN IN MILK 
FROM FAT 

Rule. — To find the per cent, of casein in milk when 
the per cent, of fat is known, subtract 3 from the per 
cent of fat in milk, multiply the result by .4 and add 
this result to 2.1. Example: How much casein is there 
in milk containing 4.5 per cent, of fat? (4.5 — 3)x.4+ 
2.1=2.70 per cent of casein. 

This rule is based upon the writer's work, showing 
that milk testing 3 per cent of fat contains an average 
of about 2.1 per cent of casein, and that the casein in- 
creases, on an average, .4 per cent, when the per cent, 
of milk increases i per cent, above 3. This is especially 
true of milks ranging from 3 to 4.5 per cent, of fat 
when the milk is produced at the same stage of lacta- 
tion. In the later stages of lactation the ratio of ca- 
sein to fat is greater than is indicated by this rule. 
(See p. 12.) 

In applying Rule 9, Rule 10 can be used to find 
the per cent, of casein in milk when only the per cent, 
of fat is known. For example, how much cheese can 
be made from 100 pounds of milk containing 4.25 per 
cent, of fat? By Rule 10, (4.25 — 3)x.4+2.i=2.6, the 
per cent, of casein in the milk. Then by Rule 9, (2.6 
x2.5)+(4.25xi.i) = ii.i8 pounds. 

The above rule can be used in finding the amount 
of casein and albumin together, the factor 2.9 being 
added instead of 2.1. 



ARITHMETIC OF MILK AND MILK PRODUCTS I93 

11. FINDING YIELD OF CHEESE FROM FAT AND 
LACTOMETER 

Rule. — To find how much green cheese can be made 
from 100 pounds of milk when the per cent, of fat in 
milk and the lactometer reading are known, Und the 
per cent, of solids-not-fat by Rule 4, divide the re- 
sult by 3 and to this add the per cent, of fat multiplied 
by .91, and finally multiply the result by 1.58. 

This rule was devised by Dr. Babcock and gives 
good results- It may be expressed also in the follow- 
ing form: (•!2»££:E!2H^ + fat X .91) X 1.58. 

EXAMPLES FOR PRACTICE UNDER RULES 
8 TO 11 

(i) What is the per cent, of casein in milk contain- 
ing (a) 3.50, (b) 3.60, (c) 4, (d) 4.4 per cent, of fat? 

(2) How much green cheese should be made from 
100 pounds of the different milks mentioned in the 
preceding example? (Apply Rule 9 and Rule 10). 

(3) How much green cheese should be made from 
18,000 pounds of milk testing 3.75 per cent, of fat? 

(4) How much green cheese should be made from 
100 pounds of milk testing 4 per cent, of fat and show- 
ing a lactometer reading of 33? 

(5) What is the per cent, of casein and albumin in 
milk containing (a) 3.50, (b) 3.80, (c) 4.30, (d) 5 
per cent, of fat? 

12. FINDING DIVIDENDS ON FAT BASIS AT 
CREAMERIES 

Rule. — To calculate the amount of each patron's 
dividend at creameries on the basis of the fat in the 
milk, multiply the amount of the milk-fat delivered by 
each patron by the price of one pound of fat. 



194 



MODERN METHODS OF TESTING MILK 



This rule can be made more clear by considering 
the process in three separate steps, assuming that the 
creamery is operated on the co-operative plan. 

Step I. By Rule i find the amount of milk- fat fur- 
nished by each patron during the dividend period. 

Step 2. Find the net value of one pound of milk- 
fat by dividing the total net receipts by the total num- 
ber of pounds of fat delivered by all the patrons during 
the dividend period. 

Step 3. Multiply the number of pounds of fat de- 
livered by each patron by the net price received for 
one pound of fat. 

Example: Step i. The data and results are indicated 
in tabular form as follows: 





Pounds of Milk 




Per cent. 




Pounds of 


NAME OF 


delivered during 


offat 




fat in milk 


PATRON 


dividend period 




in milk 




delivered 


A . . 


• - 350 


X 


4.0 


= 


14.00 


B . . 


• . 650 


X 


3-6 


— 


23.40 


C . . 


. . 835 


X 


5-2 


■=. 


43.42 


D . . 


. .965 


X 


44 


= 


42.46 


E . . 


. . 1,200 


X 


4.2 


= 


50.40 


Total number of pounds 


of fat delivered 


by 






all na 


irons . . . 


, 




. 


173.68 



Step 2. From the amount of fat indicated above, 
the amount of butter made was 195 pounds, which 
realized 18 cents a pound after deducting all expenses, 
making a total of $35.10. This sum divided by 173.68, 
the total pounds of fat delivered, gives 20.2 cents as 
the net price received for each pound of fat. 



ARITHMETIC OF MILK AND MILK PRODUCTS I95 

Step 3. The data and results are indicated in tabu- 
lar form, as follows : 





Pounds 




Net price 




A mount of 


NAME OF 


of fat 




received for fat 




dividend due 


PATRON 


delivered 




per pound 




each patron 


A . 


. 14.00 


X 


20.2 cents 


= 


$2.83 


B . 


. 23.40 


X 


" " 


rz 


473 


c . 


. 4342 


X 


il ct 


= 


8.77 


D . 


. 42.46 


X 


il ii 


= 


8.58 


E . 


50.40 


X 


" " 


=z 


10.18 



When both milk and cream are used in a creamery, 
the pounds of fat delivered in the form of cream are 
found by applying Step i above and then multiplying 
the result by 1.02. From this point on, the process of 
calculating dividends is the same as above described. 

13. FINDING DIVIDENDS ON FAT BASIS AT 
CHEESE-FACTORIES 

Rule. — To calculate the amount of each patron's 
dividend at cheese-factories on the basis of the fat in 
the milk, proceed as under Rule 12. 

14. FINDING AMOUNTS OF MILK, ETC., TO USE 
IN MODIFYING NORMAL MILK 

The practice of modifying or standardizing milk 
for special market purposes is constantly increasing. 
This consists in increasing or decreasing the per cent, 
of fat in a normal milk. The per cent, of fat in a 
normal milk may be increased (i) by adding cream, 
(2) by adding milk richer in fat, or (3) by skimming 
part of the normal milk with a separator and then put- 
ting the cream thus obtained back into the rest of the 
normal milk. The per cent, of fat in a normal milk 



196 MODERN METHODS OF TESTING MILK 

may be decreased without adding water, (i) by add- 
ing skim-milk, (2) by adding milk poorer in fat, or 
(3) by skimming part of the milk and then putting 
the skim-milk thus obtained back into the rest of the 
normal milk. 

Prof. R. A. Pearson, of Cornell University, has de- 
vised an ingenious method by which one can accu- 
rately, quickly and easily find the amounts of milk, 
cream and skim-milk to be used in modifying or stand- 
ardizing milk in order to produce a milk containing a 
desired per cent, of milk-fat. The following diagram 
and explanation may serve to make clearer the work- 
ing of the method: 

Milk 



Per cent, fat in milk=A 



Per cent, fat in 
cream, etc. 



Per cent, fat in 



modified milk 



C— B or B-— C (pounds of A to use 



Cream or skim- 
milk, etc. 



A— B or B— A (pounds of C to use) 



Let A represent the per cent, of fat in the milk 
to be modified. 

Let B represent the per cent, of fat desired in the 
modified milk. 

Let C represent the per cent, of fat in the milk, 
cream or skim-milk which is to be used in increasing 
or decreasing the per cent, of fat. 

The problem is to find in what proportions we shall 
use the milk, etc., containing A and C, in order to ob- 
tain a product containing B. 

When the per cent, of fat in the normal milk is 
to be increased, A is less than B, while C is greater 
than B. In this case, B minus A gives the pounds of 



ARITHMETIC OF MILK AND MILK PRODUCTS I97 

the product containing C to be used, while C minus B 
gives the pounds of milk (A) to be used or, expressed 
in another way, the procedure becomes, B — A=pounds 
of product containing C to be used, and C — Expounds 
of milk (A) to use. 

When the per cent, of fat in the nonPxal milk is 
to be decreased in the modified milk, the procedure is 
thus indicated: A — B=pounds of product containing 
C to be used and B — C=pounds of milk (A) to be 
used. 

The simplicity of the method becomes readily ap- 
parent when practically illustrated. 

(i) When the per cent, of fat in milk is to be in- 
creased by addition of cream or richer milk. Rule. — 
From the per cent, of fat desired in the modified milk 
subtract the per cent, of fat in the milk to be modified, 
and the result is the number of pounds of cream or 
richer milk to be used. From the per cent, of fat in 
the cream or richer milk subtract the per cent, of fat 
desired in the modified milk, and the result is the num- 
ber of pounds to use of the milk to be modified. Ex- 
ample : What relative amounts of normal milk and 
cream must be used to produce milk containing 4.5 
(B) per cent, of fat, when the normal milk contains • 
3.5 (A) per cent, of fat and the cream 25 (C) per 
cent. ? 

Milk 



A=3.5 '—^ C— B=2o.5 (pounds of milk to use). 

B=4-5 

B— A=i (pounds of cream to use). 



C=25 



Cream 

The results mean that 20.5 pounds of milk contain- 
ing 3.5 per cent, of fat, mixed with i pound of cream 
containing 25 per cent, of fat, will produce a modified 



198 MODERN METHODS OF TESTING MILK 

milk containing 4.5 per cent, of fat. If, in place of 
cream, a milk containing more than 3.5 per cent, of 
fat were used, the process would be the same. 

(a) If it is desired to know how much such cream 
must be used in standardizing 1,000 pounds of such 
milk, divide 1,000 by 20.5 (C — B) and multiply by 
I (B — A,) which will give 48.8 pounds of cream to be 
added and 1048.8 pounds of the modified milk. 

(b) If it is desired to know how much such cream 
and milk to use to make 1,000 pounds of the modified 
milk, divide 1,000 by 21.5 (C — B) + (B — A), which 
is 46.5, and multiply this amount by 20.5 (C — B) and 
by I (B — A), which will give 953.5 pounds of 3.5 
per cent, milk and 46.5 pounds of 25 per cent, cream. 

(2) When the per cent, of fat in milk is to be in- 
creased by removing a portion of the milk-serum 
(skim-milk). Rule. — From the per cent, of fat de- 
sired in the modified milk subtract the per cent, of fat 
in the milk to be modified, and the result is the number 
of pounds of skim-milk to be removed. The per cent, 
of fat in the modified milk is the number of pounds to 
use of the milk to be modified. This is done by sep- 
arating the cream from a portion of the milk and then 
adding it to the normal milk. The skim-milk can be 
assumed to contain practically no fat. Example : How 
much skim-milk should be removed from milk con- 
taining 3.9 per cent, of fat, in order to produce a mod- 
ified milk containing 5 per cent, of fat? 

Milk 
A=3.9 B— C=5 (pounds of milk to use). 



B=5 



C=o.oL 



Skim-milk 



B — A=-=i I (pounds of skim-milk to remove). 



ARITHMETIC OF MILK AND MILK PRODUCTS I99 

In this case we add nothing, so that C equals o and 
B — C=:5 — 0^5. The results mean that for 5 pounds 
of the milk, we should remove i.i pounds of skim- 
milk, thus reducing 5 pounds of milk containing 3.9 
per cent, of fat to 3.9 pounds of modified milk contain- 
ing 5 per cent, of fat. 

Applying these results to a specific case, how much 
skim-milk should be removed from 980 pounds of 
3.9 per cent, milk to increase the fat to 5 per cent? 
Divide 980 by 5 (B — C), which gives 196, and mul- 
tiply this by I.I (B — A) which gives 215.6 pounds of 
milk-serum or skim-milk to be removed, leaving 764.4 
pounds of modified 5 per cent. milk. 

(3) When the per cent, of fat is to he decreased by 
adding skim-milk. Rule — From the per cent, of fat 
in the milk to be modified subtract the per cent, of fat 
desired in the modified milk, and the result is the num- 
ber of pounds of skim-milk to be used. From the per 
cent, of fat desired in the modified milk, subtract the 
per cent, of fat in the skim-milk, and the result is the 
number of pounds to use of the milk to be modified. 
Example: How much skim-milk containing .1 per 
cent of fat should be added to milk containing 5 per 
cent, of fat to reduce the fat to 3.9 per cent.? 

Milk 
A=5 B— C=3.8 (pounds of 5 per cent. milk). 



B=3.9 



Skim-milk 



A — B=i.i (pounds of skim-milk). 



(a) How much skim-milk should be added to i,ooo 
pounds of 5 per cent, milk to produce 3.9 per cent, 
milk? Divide 1,000 by 3.8, giving 263, and multiply 
the result by i.i, which gives 289, the number of 



200 MODERN METHODS OF TESTING MILK 

pounds of skim-milk. There would be 1,289 pounds 
of 3.9 per cent. milk. 

(b) How much skim-milk is needed to produce 
1,000 pounds of modified 3.9 per cent, milk? Divide 
1,000 by 4.9, which gives 204.08. This, multiplied by 
3.8, gives 775.5 pounds of 5 per cent, milk to use and, 
multiplied by i.i, gives 224.5 pounds of skim-milk. 

EXAMPLES FOR PRACTICE 

(i) What amount of milk containing 4.7 per cent 
of fat, and of cream containing 30 per cent, of fat, 
should be mixed in order to produce 740 pounds of 
milk containing 6 per cent, of fat? 

(2) Mix milk containing 5.2 per cent, of fat with 
milk containing 3.3 per cent of fat in such amounts 
as to produce 950 pounds of milk containing 4.1 per 
cent, of fat. 

(3) How many pounds of separator skim-milk must 
be mixed with 100 pounds of cream containing 20 
per cent, of fat in order to produce a modified milk 
containing 5 per cent, of fat? 

(4) How many pounds of skim-milk must be mixed 
with two pounds of 4.5 per cent, milk in order to pro- 
duce a mixture containing 3 per cent, of fat? 

(5) How much skim-milk must be removed from 
milk containing 3 per cent, of fat in order to increase 
the fat to ^.y per cent.? 

15. CORRECTING QUEVENNE LACTOMETER 
READING FOR TEMPERATURE 

Rule. — For each degree F. above 60° F. add .1, and 
for each degree belozv 60° F. subtract .1 (See p. 123). 



ARITHMETIC OF MILK AND MILK PRODUCTS 20I 

16. CONVERTING QUEVENNE INTO BOARD OF 
HEALTH LACTOMETER DEGREES 

Rule. — Divide the Quevenne reading by .29. (See 
p. 126.) 

17. CONVERTING BOARD OF HEALTH INTO 
QUEVENNE LACTOMETER DEGREES 

Rule. — Multiply the Board of Health reading by 
.29. (See p. 126.) 

18. CORRECTING BOARD OF HEALTH LACTOM- 
ETER READING FOR TEMPERATURE 

Rule. — For each degree F. of temperature above 
60° F. add .3, and for each degree below 60° F. sub- 
tract .3. (See p. 128.) 

19. CHANGING VOLUME INTO WEIGHT 

Rule. — To convert a known vohime of a Hquid 
into pounds when the specific gravity is known, mul- 
tiply the speciHc gravity of the liquid by the zveight 
of an equal volume of zvater. Example : One gallon of 
water weighs 8.33 pounds; what is the weight of a 
gallon of milk whose specific gravity is 1.032? Mul- 
tiplying 8.33 by 1,032, we have as the answer 8.6 
pounds. 

20. CHANGING POUNDS OF MILK INTO QUARTS 

Rule. — Divide the number of pounds of milk by 2.1^. 
Example: How many quarts of milk in 100 pounds? 
iocK-2i5.=46.5 quarts. 



202 MODERN METHODS OF TESTING MILK 



21. CHANGING QUARTS OF MILK INTO POUNDS 

Rule. — Multiply the number of quarts by 2.15. Ex- 
ample : How many pounds in 40 quarts of milk ? 40 
X2. 15^86 pounds. 

22. CHANGING DEGREES FAHRENHEIT INTO 

DEGREES CENTIGRADE 

Rule. — From the degrees F. subtract 32 and mul- 
tiply the result by 5-9. Example: 162° F.=r(i62 — 32) 

X5-9=:72° C. 

23. CHANGING DEGREES CENTIGRADE INTO 

DEGREES FAHRENHEIT 

Rule. — Multiply the degrees C. by 9-5 and add 32. 
Example: y2° C.= ( 72x9-5 )+32= 162° F. 



24. FINDING THE TRUE AVERAGE 

Rule. — To find the true average per cent, of fat in 
different lots of milk or milk products, find the weight 
of fat in each separate lot by Rule i, add these amounts 
and divide the sum by the total weight of milk or milk 
products. Example: What is the average per cent, 
of fat in the following lots of milk? 

Founds Per cent. Pounds 

of 7nilk of fat of fat 

400 containing 4.3 i7-2 

300 " 34 10-2 

800 " 5-2 41-6 

100 " 31 • 31 

1,600 72.1 



ARITHMETIC OF MILK AND MILK PRODUCTS 203 

Applying Rule i, we find the weight of fat in each 
lot of milk, the results being indicated in the third 
column above. The total amount of fat in all of the 
milks is 72.1 pounds, which, divided by 1,600 (the 
total weight of milk), gives 4.5 as the real average 
per cent, of fat in all the milk. 

It is wrong to regard as the average per cent, the 
result obtained by adding the per cents, directly and 
then dividing this sum by the number of lots repre- 
sented, unless the amounts of milk or milk products 
are equal. Thus, in the foregoing example, the result 
of such a wrong method would make the average 4 
per cent., when it is really 4.5. 

The same principle explains why we do not get a 
true average composite sample, when we take the 
same amount of milk from different lots that vary 
considerably in weight and per cent, of fat. 

EXAMPLES FOR PRACTICE 

( 1 ) Find the average per cent, of fat in the follow- 
ing lots of milk: 1,200 pounds, 3 per cent, of fat; 
2,000 pounds, 5 per cent, of fat ; 6,000 pounds, 4 per 
cent, of fat; and 1,800 pounds, 3.5 per cent, of fat. 

(2) Find the average per cent, of fat in 1,000 
pounds of cream, 40 per cent, of fat; 1,600 pounds, 30 
per cent, of fat; and 400 pounds, 20 per cent, of fat. 

25. FINDING AMOUNT OF CREAM 

Rule. — To find the amount of cream produced for 
100 pounds of milk when the per cent, of fat in milk 
and in cream is known, divide the per cent, of fat in 



204 MODERN METHODS OF TESTING MILK 

milk by the per cent, of fat in cream and multiply the 
result by loo. Example: How many pounds of 
cream containing 25 per cent, of fat are produced 
from 100 pounds of milk containing 5 per cent, of fat? 
5-^25=.2. .2x100=20, number of pounds of cream 
with 25 per cent, of fat. 



26. FINDING AMOUNT OF SKIM-MILK 

Rule. — To find the amount of skim-milk for 100 
pounds of milk when the per cent, of fat in milk and 
in cream is known, Und the amount of cream by Rule 
25 and then subtract this from 100. Example: How 
much skim-milk is produced from 100 pounds of milk 
containing 4 per cent, of fat when the cream contains 
25 per cent of fat? 4-^25=. 16; .16x100=16; 100 — 
16=84, number of pounds of skim-milk. 

27. FINDING AMOUNT OF BUTTERMILK 

Rule. — To find the amount of buttermilk for 100 
pounds of milk when the per cent, of fat in milk and 
in cream is known, multiply the amount of fat in 100 
pounds of milk by 1.17 and subtract the result from 
the amount of cream. Example: How many pounds 
of buttermilk are produced for 100 pounds of milk 
containing 4 per cent, of fat, when the cream used 
contains 25 per cent, of fat? 4x1.17=4.68 (pounds 
of butter made) ; 4-^-25x100:= 16 (pounds of 25 per 
cent, cream) ; 16 — 4.68=11.32 (pounds of buttermilk). 



ARITHMETIC OF MILK AND MILK PRODUCTS 205 

28. FINDING SPECIFIC GRAVITY OF 
MILK-SOLIDS 

Rule. — To find the specific gravity of milk-solids, 
when the specific gravity of the milk and per cent, of 
milk-solids are known, multiply the specific gravity of 
the milk by loo, from the result subtract loo and di- 
vide this result by the specific gravity of the milk. Sub- 
tract the last result from the per cent, of milk-solids 
and then divide this result by the per cent, of milk- 
solids. (See p. 131.) 

29. FINDING AMOUNT OF ADDED WATER 
IN MILK 

See page 134. 

30. FINDING AMOUNT OF MOISTURE IN BUTTER 

Rule. — To find the approximate amount of mois- 
ture in butter, add j to the per cent, of fat (obtained 
by the method described on p. 82) and subtract the 
sum from 100. In adding 3, allowance is made for 
I per cent, of casein and 2 per cent, of salt in the 
butter. The results by this method should in most 
cases be within i or 2 per cent, of the correct fig- 
ures. Example: How much moisture in butter con- 
taining 83.7 per cent, of fat? 83.7+3=86.7; 100 — 86.7 
= 13.3, the per cent, of moisture. 

31. TABLE SHOWING APPROXIMATE EQUIVA- 

LENTS OF METRIC SYSTEM 

I fluid ounce = 29.60 cubic centimeters (cc.) 

I quart = 0.95 liter (1.) 

I gallon = 3.8 liters. 

I grain = 65. miligrams (mg.) 

I ounce (av.) = 28.35 grams (gm.) 

I pound = .45 kilogram (kg.) 



INDEX 



PAGE 

Acid, lactic, from milk-sugar . . 13 

Estimation of 88-100 

Acid, sulphuric, action in Babcock 

test 33 

Adding to milk 56 

Care in handling 44 

Effect of strong and weak acid . 42 

Measuring for test 56 

Mixing with milk 58 

Strength of 42 

Temperature when used .... 57 

Testing strength of 43 

Acid-hydrometer 43 

Acid-measures 36, 37 

Testing accuracy of 49 

Acid solution 90 

Acid tester 43 

Acid tests, Mann's 93 

Spillman's 97 

Acids, action on alkalis 89 

In milk-fat 3 

Volatile acids 4 

Acidity, indicators for 90 

In milk, causes and kinds of . . 88 

In milk in relation to bacteria . 105 

In rich and poor cream .... 102 

Principles of testing 89 

Rapid estimation of 98 

Testing of, in cheese 102 

In cream and milk 93-100 

In whey 101 

Acidometer 43 

Adulterations of butter 141 

Cheese 142 

Cream 140 

Milk 133 



PAGE 

Age of composite samples when 

tested 31 

Of milk, testing by rennet ... 118 

Albumin in milk 11 

In relation to casein 12 

Alkalis, action on acids 89 

Alkali test, Purdue 99 

Alkaline solution 90 

Alkaline-tablet test 95 

Analysis. See Composition. 

Annatto, detection of, in milk . . 139 

Apparatus in Babcock test ... 34 

Testing accuracy of 45 

Appearance in judging and scor- 
ing butter 159 

Cheese 172 

Arithmetic of milk and products . 185 

Ash in milk 13 

Average, true, how to find .... 202 

Babcock test 32 

Acid measure 36 

Acid used in 42 

Action of acid 33 

Apparatus 34 

Benefits of use 32 

Bottles 34, 70, 79 

Centrifugal machines .... 38-40 

For butter 82 

For buttermilk 80 

For cheese 80 

For condensed milk 83 

For cream 69 

For milk 53 

For milk powder 86 

For skim-milk 78 

207 



208 



MODERN METHODS OF TESTING MILK 



PAX5E 

Babcock test 

For whey 78 

Modifications of 66 

Operation of 53 

Pipette 35 

Principles underlying ..... 33 

Reading results 61 

Testers 38 

Testing accuracy of apparatus 45 

Use of centrifugal force .... 33 

Water used in 60 

Bacteria and acidity of milk ... 105 
Bacterial condition of milk, test- 
ing 105 

Bichromate of potash as preser- 
vative 29 

Board of Health lactometer ... 125 

Body of butter 154 

Of cheese 168 

Borax in milk, detection of . . . 140 
Bottles, Babcock test, for cream, 70, 71 

For milk 34 

For skim-milk, whey, etc ... 79 

Butter, appearance in judging . . 159 

Body of 154 

Calculating dividends for . . . 193 

Calculating water in 205 

Classes of 162 

Color of 156 

Commercial testing, judging, 

and scoring 150 

Composition of 16 

Definition of 18 

Finish of 159 

Flavor of 151 

Grades of 163 

Judging 150 

Moisture in 155 

" Overrun," how to calculate . 188 

Package 159 

Qualities of 151 

Renovated 18, 141 

Salt in 158 

Sampling for fat-test 82 

For judging and scoring . . . 150 

Scale of points IGO 

Score-cards 160 



PAGE 

Butter, Scoring 159 

Standard of 18 

Texture of 153 

Yield of, how to calculate ... 189 
Butter-fat. See Milk-fat. 

Buttermilk, composition of . . . 16 

Testing fat in 80 

Yield of, calculating 204 

Butter-trier 151 

Butyrometer, Gerber's 67 

By-products of milk, composition 

of 16 

Calcium casein 9 

Calibration of glassware .... 45 
Casein in milk, action of a«ids on 9 

Of alkalis 10 

Of heat 10 

Of rennet 10 

Calculating amount of, from fat 

in milk . 192 

Composition of 9 

Lactate 10 

Per cent, in milk 12 

Products formed from 11 

Proportion to albumin 12 

Centigrade degrees calculating to 

Fahrenheit 202 

Centrifugal force in Babcock test 33 

Machines 38 

Centrifuges 38, 40, 110 

Cheddar cheese, American, com- 
position of 16 

Commercial testing, judging, 

and scoring 165, 173 

Cheese, adulterations of 142 

Appearance and finish of . . . 172 

Body of 168 

Calculating yield of, from fat . 190 

From fat and casein 191 

Classes of 173 

Color of 170 

Commercial judging, testing, 

and scoring of 165 

Commercial qualities of ... . 165 

Composition of 16 

Definition of 19 



INDEX 



209 



PAGE 

Cheese 

Dividends from, calculating . . 195 

Finish of 172 

Flavor of 165 

Judging of 165 

Package 172 

Salt in 171 

Sampling for fat-testing .... 81 

For judging and scoring ... 165 

Score-cards 173 

Scoring 173 

Standard 19 

Testing acidity in 102 

Testing commercial qualities . 165 

Testing: fat in 80 

Texture 167 

Trier for sampling 165 

Yield of, calculating 190 

Cheese-factory, calculating divi- 
dends of 195 

Chemistry of cows' milk 1 

Churned samples of milk .... 21 

Prevention of 22 

Sampling of 21 

Cleaning greasy glassware ... 49 

Collecting sediment in milk . . . 109 

Coloring matter in milk, detec- 
tion of 139 

Commercial testing, judging, and 

scoring of butter 150 

Of certified milk 183 

Of cheese 165 

Of cream 183 

Of milk 174, 179 

Of standardized milk 183 

Composite samples, age for test- 
ing 31 

Care of . . 30 

Description 24 

Method of taking 26 

Preserving 28 

Sampling for test 54 

Sample-jars 25 

Composition of butter 16 

Buttermilk 16 

Casein 9 



PAGE 

Composition of Cheese 16 

Milk 15 

Milk-fat 3 

Skim-milk 16 

Whey 16 

Condensed milk, testing fat of . . 83 
Corrosive sublimate as preserva- 
tive 28 

Cows, testing on farm .143 

Cows' milk, analyses of 15 

Chemistry of 1 

Composition of 15 

Definition of 16 

Standard of 17 

Cream, acidity of, testing . . 88, 104 

Adulterations of 140 

Bottles, bulb-necked ...... 70 

Straight-necked 71 

Calculating yield of 203 

Color of fat-column 64 

Commercial testing, scoring 

and judging 183 

Definition of 18 

Keeping samples of 73 

Method of sampling 72 

Poor and rich, acidity in ... . 102 

Preparing sample for testing . 73 

Standard 18 

Testing fat in 69-76 

Weighing sample of 75 

Cream scales 72 

Creamery dividends, calculation 

of 193 

Curd-test, Wisconsin 106 

Cylinder, for lactometer 125 

Spillman's, acid- test 79 

Definitions of milk and milk prod- 
ucts 16-19 

Detection in milk, of annatto . . 139 

Borax 140 

Coloring matter 139 

Formalin 139 

Of skimmed milk 136, 138 

Of watered milk 133, 138 

Dipper, sampling 27 



210 



MODERN METHODS OF TESTING MILK 



PAGE 

Dirt in milk, testing 109 

Dividends, calculating, at cream- 
eries 193 

At cheese-factories 195 

Double-necked test-bottles .... 79 

Draining-rack 51 

Farm, testing milk on 143 

Farrington's alkaline-tablet test . 95 

Bottle-cleaner 51-52 

Fat in milk. See milk-fat. 

Fat-column, black particles in . . 64 

Gas-bubbles in 65 

Measuring, in cream-testing . . 77 

White particles in 65 

Fat-globules, in milk, number . . 4 

Size 4 

Influences affecting 5 

In cheese, etc 5 

Fermentation test of milk, Wis- 
consin 106 

Gerber's 109 

Finish of butter 159 

Of cheese 173 

Flavor of butter 151 

Cheese 165 

Milk, cream, etc 181 

Formalin in milk, as preserva- 
tive 29 

Detection of 139 

Frozen milk, sampling of ... . 23 

Galdctase in milk 11 

Gases in milk 14 

Gerber's butyrometer 67 

Fermentation test 109 

"Sal" test 68 

Glassware in Babcock test, cali- 
bration of 45 

Cleaning of 49 

Testing accuracy of 45 

Globulin in milk 11 

Glycerin in milk-fat 3 

Grades of butter 163 

Of cheese 173 

Greiner's automatic pipette ... 36 



PAGE 

Hand-testers 39, 110 

Hydrometer for testing specific 

gravity 122 

Testing strength of acid .... 43 



Infant foods, testing fat in . 
Indicator in testing acidity 



Jars, waste, for emptying test- 
bottles 50 

Jars, for composite samples ... 25 

Judging butter 150-159 

Cheese . 165-173 

Cream 183 

Milk 174-183 

Kumiss, definition of 19 

Lactate, casein 10 

Lactic acid in milk 13, 88 

Estimation of 88-100 

From milk sugar 13 

Lactose 13 

Lactometer, application . . . 119-132 

Board of Health 125 

Bichromate, effect on 128 

Cylinder for 125 

Method of using . 123 

Quevenne 122 

Temperature, effect on . . 121, 123 

Mann's acid test 93 

Marschall rennet test 115 

Measures for acid 36 

Measuring, acid 56 

Fat-column in testing cream . 77 

In testing milk 63 

Metric system, equivalents of . . 206 

Milk, acidity of 88 

Adding acid to 56 

Adulteration of 133 

Age of, testing 118 

Albumin in 11 

Analyses of 15 

Arithmetic of 185 

Ash in 13 



INDEX 



211 



PAGE 

Milk, Chemistry of 1 

Churned, sampling of 21 

Color of 179, 181 

Certified, judging 183 

Composite sampling of ... . 24 

Composition of 15 

Condensed 17, 83 

Definition of 16 

Detection of adulterations in . 133 

Flavor of 178, 181 

Frozen, sampling of 23 

Gases in 14 

Judging and scoring 182 

Keeping power of 176, 18o 

Mixing with acid 58 

Modified, to prepare 195 

Nitrog-'n compounds of ... . 8 

Salts in 13 

Sampling of 20-31 

Sampling with pipette 54 

Scale of points in judging ... 182 

Scoring of 182 

Skimmed, detection of . . . 136, 138 

Sour, sampling of 23 

Souring of 13 

Specific gravity of 119 

Standard of .' . . . 17 

Standardized, to prepare ... 195 
Standardized, judging and scor- 
ing 183 

Temperature for testing .... 57 
Terms used in judging and scor- 
ing 17P 

Testing acidity of 88-100 

Total solids of 3, 129 

Watered, detection of . . . 133, 138 

Milk-albumin 11 

Milk-bottle, use of in cream-testing 69 

Milk, Casein. See Casein. 

Milk-fat, color of in Babcock test 64 

Composition of 3 

Definition of 18 

Glycerin in 4 

Influenced by various conditions 5-8 
In relation to butter yield . . .189 
In relation to Casein 192 



PAGE 

Milk-fat, in relation to Cheese . . 190 
Method of testing, in butter. . . 82 

In buttermilk 80 

In cheese 80 

In condensed milk 83 

In cream 69-77 

In milk 53-66 

In milk powders 86 

In skim-milk 78 

In whey 80 

Per cent, in foremilk 8 

In strippings 8 

Standard of 18 

Variation of, in milk 5 

Volatile acids in 4 

Milk-globulin 11 

Milk, measuring with pipette . . 54 

Milk powders, testing of 86 

Milk products, arithmetic of . . 185 

Composition of 16 

Judging and scoring of . . 150-183 

Milk serum 15 

Milk-solids, composition of . . 3, 14 
Estimating by lactometer . . . .129 

Specific gravity of 131 

Milk-sugar 13 

Milk testing, Babcock test . . .32, 53 

On the farm 143 

Mixing milk and acid 58 

Moisture. See water. 

Monrad rennet-test ..;.... 113 

Neutral solutions 90 

Neutralization 89 

Nitrogen compounds in milk ... 8 

In relation to fat 12, 136 

New York Board of Health lac- 
tometer 125 

Oleomargarin, test for 141 

" Overrun" in butter,how to find 188 

Package, judging and scoring of, 

in butter 159 

in cheese 172 

Per cent, of any constituent of 
milk and products, how to find 186 



212 



MODERN METHODS OF TESTING MILK 



PAGE 

Percentages, average, how to find 202 

Phenolphthalein as indicator . . 90 

Pipette, in Babcock test 35 

Accuracy of, testing 49 

Correct way to use 55 

Greiner's 36 

In cream testing 75 

Sampling milk with 54 

Wagner's 36 

Potassium bichromate 29 

Pounds, to change to quarts . . . 201 
Powdered milk, testing of ... . 86 
Preservatives for composite sam- 
ples 28 

Detection of, in milk 139 

Purdue alkali test 99 

Qualities, commercial, of butter . 151 

cheese 165 

Milk 179 

Cream 183 

Quarts, to change to pounds . . 202 
Quevenne lactometer, description 

of 122 

Correcting for temperature . . 123 

How to use 123 

Compared with Board of Health 
lactometer 127 

Rack, draining for test-bottles . 51 
For composite samples .... 26 

Rennet-test, Marschall's 115 

Monrad's 113 

Renovated butter, definition of . 18 

How to detect . 141 

Standard of 19 

Richmond's slide-rule for finding 
milk-solids 130 

Russian test for fat in milk and 
products 66 

"Sal" test for fat in milk, etc., 

Gerber's 68 

Salt in butter, commercial judg- 
ing and scoring 158 

In cheese 171 

Salts in milk 13 



PAGE 

Samples. See Composite samples. 

Sampling butter 82, 150 

Cheese 81, 165 

Cream 72 

Milk, composite 24 

Frozen . 23 

Partially churned 21 

Partially creamed 20 

Sour . 23 

With pipette 54 

Sampling-dipper 27 

Sampling-tubes 27 

Scales for weighing cheese, cream, 
etc 72 

Score-cards for butter 160 

Cheese 173 

Scoring butter 159 

Cheese 173 

Cream 183 

Milk 182 

Standardized milk 183 

Sediment in milk, how to test for 109 

Serum of milk 15 

Solids of 15 

Sinacid test for fat in milk, etc. . 67 

Skim-milk, composition of ... . 16 

Detection of 136, 138 

How to calculate yield of . . . 204 

Test-bottles 79 

Testing for fat in 78 

Slide-rule, Richmond's for calcu- 
lating solids 130 

Sodium carbonate in milk, detec- 
tion of 140 

Solids-not-fat in milk 15 

How to find amount of 129 

Solids, total, in milk. See Milk- 
solids. 

Sour milk, cause of 13 

Sampling of 23 

Specific gravity of milk 119 

Cylinder 125 

Effect of fat on 120 

Effect of temperature on . . . 121 

Effect of water on 120 

How to find 121 



INDEX 



213 



PAGE 

Specific gravity, of milk solids . 131 
Table for temperature correc- 
tion 124 

Speed of testers 40 

Spillman's acid-test cylinder . . 97 

Standard of butter 18 

Butter-fat 18 

Cheese 19 

Condensed milk 17 

Cream 18 

Milk-fat 18 

Standard of Renovated butter . . 19 

Skim-milk 17 

Steam-turbine tester 38 

Sugar of milk 13 

Sulphuric acid. See acid. 

Sweetened condensed milk ... 17 

Table of correction of specific 
gravity for temperatures . . 124 
Equivalents of metric systems . 206 
Of degrees of Board of Health 
and Quevenne lactometers . . 127 

Temperature of acid in testing 

milk 57 

Of fat-column when read ... 02 
In relation to specific gravity . 121 
Of milk when tested 57 

Terms describing commercial 

qualities of butter 151 

Of cheese 165 

Of cream and milk 179 

Test, Babcock. See Babcock Test. 

Curd, Wisconsin 106 

Fermentation, Gerber's .... 109 

Rennet, Marschall .11-^ 

Monrad 113 

" Sal," Gerber's 68 

Russian 66 

Sinacid 67 

Test-bottles, accuracy of, testing 45 

Buib-necked, cream 70 

Calibration 45 

Cleaning 49 

Cream 70 

Double-necked 79 

Drain-rack 51 



PAGE 

Test, Milk 34 

Rinser 50 

Skim-milk 79 

Straight-necked cream .... 71 

Tester 46 

Whirhng 59 

Testers, Babcock 37 

Bottle 46 

Electrical 40 

Estimating speed of 40 

Hand 39 

Steam-turbine 38 

Testing, accuracy of test bottles, 

etc 45 

Acidity of cream, milk, etc . 88-100 

Age of milk 118 

Butter 82 

Cheese 80 

Condensed milk 83 

Cows on farm 143 

Dirt in milk 109 

Infant foods 85 

Milk powders 86 

Pepsin 117 

Rennet 113 

Texture, commercial, of butter . 153 

Cheese 167 

Titration 93 

Total solids of milk. See milk-solids. 

Trier for testing butter 151 

Cheese 165 

Tube, sampling 27 

Turbine testers 38 

Volatile acids in milk-fat .... 4 
Volume of liquid, changing to 

weight 201 

Wagner's, pipette 36 

Skim-milk bottle 79 

Waste acid jar 50 

Water, in milk, amount of ... . 1 

Causes of variation 2 

Detection of, in adulterated . . 133 
In butter, calculation of ... . 205 
In commercial testing and judg- 
ing of butter 155 



214 



MODERN METHODS OF TESTING MILK 



PAGE 

Water, in milk and milk prod- 
ucts 15, 16 

Used in Babcock test 60 

Watered milk, detection of . . . 133 
Weighing sainples of cream ... 75 
Weight of any constituent of milk 
and products, how to find . . 185 

Changing to volume 201 

Weights and measures, equiva- 
lents of metric system 206 

Whey, composition of 16 

Definition of 19 



PAGE 

Whey, Testing of 78 

Whirling test-bottles 59 

Wisconsin curd-test 106 

Yield of butter, how to calculate 189 

Buttermilk 204 

Cheese, for fat 190 

Cheese, from fat 191 

Cheese, from fat and casein . . 191 
Cheese, from fat and lactometer 193 

Cream 203 

Skim-milk 2O4 



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PROFITABLE DAIRYING 

A Practical Guide to Successful Deury Management. By C. L. PECK 

The introductory chapter of this book consists of a minute description of the 
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